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Old 07-19-2022, 07:43 PM   #1
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Thumbs up 2018 GMC 3500 DRW, Duramax, Allison, Thor 5th wheel.

I have a bit over 50,000 miles on my dually, with half of that being towing a 37' fifth wheel. I average about 10.6 +/- a bit depending on the territory and speed. My truck has no mods, altho I have toyed with an idea of new air intake system. It has never been to a shop for any defects in the mechanicals and has always passed NYS emission testing. We drove 9000 miles last summer from Delaware to New Orleans, San Antonio, San Diego, Lake Elsinore, Tuscon, Phoenix, Lake Okeechobee, and back home with not a problem. I have a hundred gallon fuel tank in the bed with an electric pump and it has saved me a ton of money in fuel costs. I replaced the front tires at about 47-48,000 miles, the rears are original and will be replaced before we go to Talladega in a couple of months. I am nearing 80 years in age and will not be buying a new rig in the future. As far as I am concerned, GMC nailed it down tight with their Duramax/Allison combo. The new 10 speed is a dream rather than a need. Too bad my 5th wheel doesn't come near close in quality. I also tow an enclosed 24' car trailer with a 40 Buick Convertible in it. This combo gets me down to 11.5 to 11.8 mpg as a rule. I usually drive 60 as a matter of rule, cruise control on. My only complaint is the type of built in electronic controlled electric brake system that is standard. I drive accordingly, especially on long downgrades. Other than that, Duramax/Allison, trouble free. I change my oil at 12-13,000 mile intervals, along with the trans and fuel filters. I have never added a quart of oil between changes, but it will be down about a quart or less.
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Old 07-21-2022, 08:00 AM   #2
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Yes, hard to beat that combo. My 2011 had continuous problems with the emissions systems as this was the first year for DEF, but I fixed that after it went out of warranty. 150,000 miles later it's just getting broken in. I have similar mileage pulling a 40 footer. That transmission is pretty much bullet proof but I did have to replace the transmission control module at around 100,000 miles. I bet your truck will last a long time. I'm 74 and will keep mine running until I can't drive anymore.
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Old 07-25-2022, 06:24 AM   #3
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Thank you for the information, its good to hear positive news.
I own a 2021 3500HD Duramax L5P with only 18k on the odometer thus far. We tow a 2021 Grand Design Reflection 303RLS. The 10 speed is nice but certainly not worth buying another truck just to have, besides it has yet to prove itself in the long haul. Your Allison 6 speed is time tested and one of the best made.
There is a man on YouTube (Charles Farmer) that owns a 2018 2500HD Duramax. He is in the RV Transport Business and he currently has over 400K on his truck. In his videos he does a great job of showing what he has had done to maintain his truck and the issues he has had. His engine and transmission are original and his truck is emissions intact.
By the way my fuel mileage towing in the Sierra and Rocky Mountains (we live in the Sierra) is 10.2 to !0.4 on average. The truck will flirt with 21 mpg on flat level highway not towing anything.
Thanks again for the report. Safe travels and enjoy every day!
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Old 07-29-2022, 04:40 PM   #4
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Quote:
Originally Posted by DelawareShaw View Post
I have a bit over 50,000 miles on my dually, with half of that being towing a 37' fifth wheel. I average about 10.6 +/- a bit depending on the territory and speed. My truck has no mods, altho I have toyed with an idea of new air intake system. It has never been to a shop for any defects in the mechanicals and has always passed NYS emission testing. We drove 9000 miles last summer from Delaware to New Orleans, San Antonio, San Diego, Lake Elsinore, Tuscon, Phoenix, Lake Okeechobee, and back home with not a problem. I have a hundred gallon fuel tank in the bed with an electric pump and it has saved me a ton of money in fuel costs. I replaced the front tires at about 47-48,000 miles, the rears are original and will be replaced before we go to Talladega in a couple of months. I am nearing 80 years in age and will not be buying a new rig in the future. As far as I am concerned, GMC nailed it down tight with their Duramax/Allison combo. The new 10 speed is a dream rather than a need. Too bad my 5th wheel doesn't come near close in quality. I also tow an enclosed 24' car trailer with a 40 Buick Convertible in it. This combo gets me down to 11.5 to 11.8 mpg as a rule. I usually drive 60 as a matter of rule, cruise control on. My only complaint is the type of built in electronic controlled electric brake system that is standard. I drive accordingly, especially on long downgrades. Other than that, Duramax/Allison, trouble free. I change my oil at 12-13,000 mile intervals, along with the trans and fuel filters. I have never added a quart of oil between changes, but it will be down about a quart or less.
I thought that the 2018 GMC had a 6 Speed? Is your truck a 2018?
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Old 07-30-2022, 08:03 AM   #5
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Cool

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I thought that the 2018 GMC had a 6 Speed? Is your truck a 2018?
Yes it is a 6 speed. I was saying that the 10 speed was a dream that I would like to have. But, my 18 is bullet proof so far and the prices of new ones are not reasonable. To put out $70k for 4 more gears is not in my cards.
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Old 07-30-2022, 04:16 PM   #6
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Quote:
Originally Posted by DelawareShaw View Post
Yes it is a 6 speed. I was saying that the 10 speed was a dream that I would like to have. But, my 18 is bullet proof so far and the prices of new ones are not reasonable. To put out $70k for 4 more gears is not in my cards.



Think again, I was looking at new pickups just for curiosity, and to make me feel good about spending a little money on my 2011, and I was shocked. A new one, like mine, is running in the 90's. Wow....I'm going to quit whining about a few bills for maintenance.
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Old 07-31-2022, 06:18 AM   #7
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the newer trucks with the L5P pull much better than any stock older truck and the trucks with the 10 speed have much better low end TQ due to upgrades dont to the turbo and and fuel tune.
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Old 07-31-2022, 07:08 AM   #8
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I have a 2015, 3500. Other than the DEF tank and parts replaced under warranty it’s been great. At 80K miles as it pretty much is only used for towing the 5th wheel. But I’m now thinking of doing much more traveling as I retired last year. I grew up when 100k on the odometer was the end of life. I’m hoping this think keeps going for many more miles.
As others, I looked at the new trucks, price is keeping me away.
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Old 07-31-2022, 02:01 PM   #9
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Howdy!

I also have a 2018 Chevrolet Duramax/Allison 3500 DRW. I have less than 40,000 miles on mine. The truck tows. 44’ to hauler with ease. The only problems I’ve had is with wheel sensors. Had one rear wheel sensor replaced. That last less than a few thousand miles. Then had both rear sensors replaced again. When the wheel sensor goes out it causes problems with the trailer breaking and stability track. The last time when both rear sensors went out I lost all trailer brakes.

“Happy Trails”
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Old 08-01-2022, 08:18 AM   #10
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Smile Trailer braking with 2018 GMC 3500

I have always had problems with the brakes on my GMC 3500 when towing. I have lost my truck brakes completely while descending a long downgrade twice now. Once, by the time we were at the bottom, the front end was so hot the steering wheel literally shook in my hands. This was using the maximum amount of gain and the retarder(?). I believe this is caused by the type of system that GM uses that automatically adjusts the amount of braking to the trailer according to the rate of deceleration that the truck is sensing. On a long downhill grade, light pedal pressure works until the truck brakes get hot, and then more pressure gets them hotter, with not enough braking to the trailer. I was an otr driver hauling haz waste, refers and dump trailers for most of my working days without an accident, other than two minors in NYC. I also part timed driving tour busses to Washington DC and NYC for several years without incident, so I know how to brake on extreem downgrades. My GMC dealer tells me that there is no cure other than disconnecting the present system and wiring in an otc system.
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Old 08-01-2022, 03:44 PM   #11
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Quote:
Originally Posted by DelawareShaw View Post
I have always had problems with the brakes on my GMC 3500 when towing. I have lost my truck brakes completely while descending a long downgrade twice now. Once, by the time we were at the bottom, the front end was so hot the steering wheel literally shook in my hands. This was using the maximum amount of gain and the retarder(?). I believe this is caused by the type of system that GM uses that automatically adjusts the amount of braking to the trailer according to the rate of deceleration that the truck is sensing. On a long downhill grade, light pedal pressure works until the truck brakes get hot, and then more pressure gets them hotter, with not enough braking to the trailer. I was an otr driver hauling haz waste, refers and dump trailers for most of my working days without an accident, other than two minors in NYC. I also part timed driving tour busses to Washington DC and NYC for several years without incident, so I know how to brake on extreem downgrades. My GMC dealer tells me that there is no cure other than disconnecting the present system and wiring in an otc system.
Am assuming you are using Tow/Haul mode and Exhaust brake, i.e. both are On while towing, especially on downgrades? Otherwise, something doesn't sound right.

I descended Raton Pass at the end of my trip last summer, and don't recall tapping the brakes to bring down speed more than a handful of times at most. And that trip was when Raton Pass was a bit treacherous with construction (may still be).

I am using the OEM/factory integrated brake controller too. And I realize you were mostly replying to chiefneon, but maybe you are having sensor issues as well?
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Old 08-02-2022, 07:00 AM   #12
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Brake issues with GMC

As for towing with the Tow/Haul mode on, and the exhaust brake(?) on while towing, it is the norm. As far as an exhaust brake goes, only the Cummins has a really good exhaust brake. My old Dodge, God rest its rusted out floors and doors, pulled and did a great job mechanically. The exhaust brake was superior to my GM horses, and low end torque was excellent. The transmission held up equally as well. I have not had a Ford diesel since 2012. I had a tri axle 5th wheel then and pulled it from New Jersey to Portland, Oregon twice to see my daughter out there. No hicccups, just needed another gear in the trans. Quit buying Fords when they started building their own diesel. I guess they all have ups and downs.

As a side note; my drivers side mirror was side swiped by a truck back in May. The mirror head was damaged, glass is intact and everything works. The junk plastic housing and the plastic chrome suffered. The mirror assembly is no longer available from GM. The repair est. is about $1135 for a lesser mirror installed. The mirror itself is quoted at $749. The replacement from GM does not have the foo chrome trim, all black plastic. Poor GM! Add in general sales taxes, which we do not have where I live, could add another $60, 70 or more to the bill.
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Old 08-02-2022, 08:22 AM   #13
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Have you looked on-line at aftermarket mirrors? Not knowing what year your truck is I spent 5 minutes looking on Amazon and here is just one of many available.https://www.amazon.com/Towing-Mirror...26&sr=8-3&th=1
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Old 08-03-2022, 05:32 AM   #14
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As for towing with the Tow/Haul mode on, and the exhaust brake(?) on while towing, it is the norm. As far as an exhaust brake goes, only the Cummins has a really good exhaust brake. My old Dodge, God rest its rusted out floors and doors, pulled and did a great job mechanically. The exhaust brake was superior to my GM horses, and low end torque was excellent. The transmission held up equally as well. I have not had a Ford diesel since 2012. I had a tri axle 5th wheel then and pulled it from New Jersey to Portland, Oregon twice to see my daughter out there. No hicccups, just needed another gear in the trans. Quit buying Fords when they started building their own diesel. I guess they all have ups and downs.

As a side note; my drivers side mirror was side swiped by a truck back in May. The mirror head was damaged, glass is intact and everything works. The junk plastic housing and the plastic chrome suffered. The mirror assembly is no longer available from GM. The repair est. is about $1135 for a lesser mirror installed. The mirror itself is quoted at $749. The replacement from GM does not have the foo chrome trim, all black plastic. Poor GM! Add in general sales taxes, which we do not have where I live, could add another $60, 70 or more to the bill.
I would have to respectively disagree that the Dodge has the only good exhaust brake. I have a 2018 Silverado and the exhaust brake works fine. I have towed my trailer out west driving mountain roads with grades as much as 12% and my exhaust brake worked excellent in maintaining my controlled speed with very little if any braking while towing my trailer. I think that you have other problems with your truck besides what you call an insufficient exhaust brake. I have never overheated my brakes and hope that if all is working in conjunction with the exhaust brake, tow haul mode and brakes that I never will overheat brakes....
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