Go Back   iRV2 Forums > TRAVEL TRAILER, 5th WHEEL & TRUCK CAMPER FORUMS > Trailer Towing and Tow Vehicles Discussion
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
Thread Tools Search this Thread Display Modes
Old 01-01-2013, 10:22 AM   #1
Junior Member
Join Date: Jan 2013
Posts: 8
losing speed on hills - diesel & fifth wheel

I recently took my new-to-me fifth wheel and truck on an interstate trip to get some experience towing. The fifth wheel is a 2007 Mountaineer, 36' and weighs ~12k lbs. The truck is a 2003 GMC Sierra 3500 dually with the 6.6L Duramax diesel. I was disappointed to find out that it was not uncommon to lose 10 mph (or even 15 mph) while going up sustained hills (starting from 65 mph). These were not huge hills or mountains, either. This was in east Georgia on I-20, if anyone is familiar with the area.

So, does this sound normal? I was surprised as everything I'd read seemed to indicate the 3500 diesel ought to be able to pull this load fine. I had the pedal floored on a lot of these hills and kept losing speed anyway. I was using the tow/haul mode. I was expecting a downshift from the transmission to compensate for the hill and hold my speed, but this didn't happen.

If this isn't normal, does anybody have suggestions on what to check or have looked at?

gtmatt is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 01-01-2013, 10:41 AM   #2
Moderator Emeritus
TXiceman's Avatar

Vintage RV Owners Club
Texas Boomers Club
Oklahoma Boomers Club
Ford Super Duty Owner
Join Date: Aug 2000
Location: Full Time, TX Home Base
Posts: 17,169
Blog Entries: 21
Have you had your codes pulled on the OBD II port to see if all is well. Also, it depends on what percent grade the hills are.

Also, have you checked the actual weight of the trailer?

My 2012 F350 Ford diesel has no troubles with "hills".


Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot
TXiceman is offline   Reply With Quote
Old 01-01-2013, 10:47 AM   #3
Senior Member
JohnBoyToo's Avatar

Monaco Owners Club
Join Date: May 2012
Location: DFW, Tex-US
Posts: 5,028

I too have lot's of questions...
Assuming there is nothing wrong with your dmax, I too would think it would do as well as my 6.7L ford...

What's the gearing /hp/ torque/ towing capacity of your TV ?
have stock tires/wheels ?

What rpms do you normally run at ?

I like to keep mine in manual 6th gear and let the turbo pull the smaller hills
but while my max tq starts @ 1600 rpms, on bigger 'hills'(> 3% for any lenght of time) I have to let it downshift to keep the rpms up above there or I too loose speed with my load...

I think you'll be ok, just learning how your truck likes to work will improve it !
good luck...
'11 Monaco Diplomat 43DFT RR10R pushed by a '14 Jeep Wrangler JKU. History.. 5'ers: 13 Redwood 38gk, 11 MVP Destiny, Open Range TT, popups, vans, tents...
JohnBoyToo is offline   Reply With Quote
Old 01-01-2013, 10:57 AM   #4
Senior Member
BFlinn181's Avatar

Gulf Streamers Club
Join Date: Jan 2012
Location: Cincinnati
Posts: 17,869
You need to find out the RPM where you get maximum torque and keep engine in this power band. Also an exhaust temp gauge to monitor how hard the engine is working is good information to know. Pay less attention to speed and more to RPM, EGT and coolant temp. and your truck will last longer and perform better.

Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI
BFlinn181 is offline   Reply With Quote
Old 01-01-2013, 12:30 PM   #5
Senior Member
Join Date: Apr 2012
Posts: 374
BF is correct. I want my duramax, pulling10k+, below 1800-2000 RPM and the EGR below 1300 degrees. Accordingly, I will manually shift to a lower gear if need be. Typically though, Im on a fairly steep/long grade and not waiting for the allison to downshift. I don't want to chance lugging the engine.
fvstringpicker is offline   Reply With Quote
Old 01-01-2013, 12:52 PM   #6
Senior Member
Franka548's Avatar
Freightliner Owners Club
Retired Fire Service RVer's
Join Date: Apr 2011
Location: N E Ohio
Posts: 3,605
Change your fuel filter, preferably with an ac delco original equipment filter. This maybe the reason for your transmission not down shifting also, although I am not positive on this one. But a partially plugged fuel filter will cause these types of problems.
05 Alfa Gold 40' Motor Home "Goldie" 03 Malibu Toad towing 4 down
03 Silverado cclb 3500 drw, D/A, Reese 22k hitch
07 Alfa SeeYa Gold 30RL,2 slides,power everything Above for sale PM me for details
Franka548 is offline   Reply With Quote
Old 01-01-2013, 01:03 PM   #7
Senior Member
Join Date: Aug 2012
Posts: 390
gtmatt is this your first rig ?? running you rig with your foot on the floor is a sure way to gut the motor ... if you don't have a prometer have one put on and drive keeping it within temp ranges. first off rving is all about the enjoyment of the trip, not how fast can i get there. i don't care how much torque you have there will always be a hill that you lose speed on. that being said you can always have your power turned up.
wonderer1 is offline   Reply With Quote
Old 01-01-2013, 01:17 PM   #8
Senior Member
Kevinc2011's Avatar
Join Date: Mar 2012
Posts: 170
On that chevy 6.6 L drive train, Have your mechanic check the turbo output. We have numerous troubles with these engines on our fleet bucket trucks!
2014 Ram 3500 CrewCab MAXTOW DRW, 2015 Forest River Dynamax Trilogy 38RL
Kevinc2011 is offline   Reply With Quote
Old 01-01-2013, 01:40 PM   #9
Registered User
KSCRUDE's Avatar
Join Date: Aug 2012
Location: The Land Of Oz RVM17
Posts: 1,592
All trucks will lose speed on hills. I have trucks with 625 HP and 2050 FPT. And they lose speed on hills and in high winds. Not a lot and it depends on load, wind and the steepness and length of the grade. And these thing have 18 speed auto tranys, and may sometimes lose 2 or 3 gears on a interstate grade. That why they have the extra slow lane on hills, for trucks and pickups pulling loads. It's just a matter of physics. There is probably nothing wrong with your truck. It's just a baby throw away diesel. (No piston liner engines are called throw away motors in the trade) I think all Power stroke engines are also. Not sure about the little cummins in the dodge pickups. Just drive it and let it do its thing. I don't even want to talk about my brand new MH with the Ford V10 and what it loses on hills.
KSCRUDE is offline   Reply With Quote
Old 01-01-2013, 02:19 PM   #10
Registered User
wincrasher's Avatar
Join Date: May 2001
Location: Greer, SC
Posts: 670
My rig is around 13,000 lbs and I set my cruise at 65 and it holds very well on all but the steepest grades. I only lost speed in 2 spots - one north of Asheville on I26 and another in West Virginia on a 5% grade. I never dropped below 60 though.

I think something must be wrong with your truck, or your trailer is alot heavier than you think.
wincrasher is offline   Reply With Quote
Old 01-01-2013, 03:42 PM   #11
Senior Member
Join Date: Sep 2012
Location: Chandler, Az
Posts: 112
I'm almost thinking his trailer is heavier than he thinks. Let us know what you find out. I'd definitely weigh the trailer first, since that's the cheapest fix.
Bigg-limo is offline   Reply With Quote
Old 01-01-2013, 09:34 PM   #12
Senior Member
Ray,IN's Avatar
Join Date: Aug 2001
Location: North America somewhere
Posts: 13,905
Your truck's Duramax engine is rated at 300HP in stock form. Your Allison transmission is properly matched to the engine through the ECM of the transmission coupled with the ECM for the engine. Read that Allison FAQ link to become more familiar with how it operates. It takes about 100 shifts for the Allison ECM to learn how to shift according to your driving habits. Tow/Haul is designed to be used when the truck is at or over 80% of maximum load according to that FAQ page.
I second replacing the fuel filter. You may order OEM fuel filters from the internet for much less than you pay at your local auto parts store or a dealer. Another item to check is the rubber connectors in the air intake pipe. If one of these develop even a tiny leak you will have little power on hills. The LB7 engine (up to mid-2004) has a well-known injector problem. Check your engine oil frequently for fuel in the oil. It is a sign at least one injector has failed.
I wouldn't worry about aftermarket gauges on stock diesel pickup. The onboard computer has safeguards in it to prevent most common diesel problems. If the exhaust gas temperature reaches 1,350*F the computer will reduce rpms and power until the temperture drops to a safe level. You will notice your "gas pedal" is not connected to the engine, it only has wires leading to the computers, which control everything for the engine and transmission. Some speed reduction on hills is normal.
For a test, next time you are towing your 5er do not engage tow/haul and remember how your truck shifts for several miles. Then engage tow/haul, and without changing your driving habits, note what changes.
The main function of GM's tow/haul feature is to reduce or eliminate "hunting" for the right gear by the transmission, which is the main source of overheating an automatic transmission.
I suggest joining dieselplace.com , a forum dedicated to the GM diesel engines. No need to post questions at first, use the search feature to find what was previously posted about your problem/questions. You have a very reliable truck. The number one rule for diesels is Keep the fuel clean!
Welcome to irv2.com! Make it a habit to return here frequently and learn; I do. I've been here since 2002 and still learn something with every visit.
Ray,IN is offline   Reply With Quote
Old 01-02-2013, 05:33 PM   #13
Senior Member
wandering1's Avatar
Join Date: Nov 2007
Location: NC
Posts: 462
Send a message via ICQ to wandering1
Get a Ford.
wandering1 is offline   Reply With Quote
Old 01-02-2013, 05:47 PM   #14
Senior Member
Vintage RV Owners Club
Fleetwood Owners Club
Join Date: Dec 2009
Location: CA
Posts: 1,092
That truck is 10 years old, do youstill have 300 horses?

P30, 454 ENG, TURBO 400 TRANS
GOLDWINGER2 is offline   Reply With Quote


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

» Featured Campgrounds

Reviews provided by

Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 02:10 AM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2018, vBulletin Solutions, Inc.