I chipped mine with the DigiCR chip after hearing the success of YC1. I even called YC1 about a year after he chipped his to make sure it didn't blow up.
On the rear radiator Monaco's, a company named Source Engineering was making newly designed engine fans. They added 25 HP on the ISL and 40 HP to the ISC (faster turning engine) by making the fan more efficient. You could probably fly an airplane with the stock fan. You can also buy a Horton electrically controlled fan for more HP, but they don't work when climbing because they're engaged.
The fan combined with the chip made my 36' Diplomat a rocket. I pulled the Baker grade into Vegas at 70 towing a 4 door Nissan Frontier. I found that the chip smoothed out the power band on the Diplomat. It would pull hard at a wider rpm range. When I traded in the coach, I removed the chip for fear that the new owner would have no idea what it was. I sold it to a friend with a Diplomat, figuring I would never be able to use it on a new DEF engine.
Well, guess what.....it's the same chip for the ISL from 05 to 2015. It will work on my new DEF engine. I will eventually buy another one (about $600.00) when my new motor has about 20K on it.
Lastly, the chip does not leave an imprint on your engine computer because it attaches to the fuel rail and changes the fuel timing. It comes with a 15' cable that allows you to plug it into the fuel rail (unplug the fuel rail electric plug, plug in the double sided chip cable and plug the fuel rail plug back in). I routed the cable into the rear closet of the bedroom so I could adjust the chip if needed. It has a dial that can be adjusted to a couple of positions. It also has a dummy plug that you can pull the chip off of the cable and plug in the dummy plug and the engine reverts back to stock. The best part, under wide open throttle (WOT) the chip reverts back to stock to prevent handgrenading the engine.
Ray....we only got good mileage on longer trips where the mileage had a chance to equal out between hill climbs and flatland. The 05 Diplomat was the last year they used the shorter 22.5" tires and it ran well at about 1480 rpm at 58 mph. When not towing we hit 10 a few times doing the fuel ups with a level coach and pencil and paper math. The Diplomat had an 8' side to side fuel tank and was hard to record mileage over short trips because some fill ups would take almost 5 gallons more because of a little lean.
The Dutch Star has a center mounted tank between the frame rails and fills more evenly. I tried driving it at 58 like the Diplomat, but the mileage was worse. I run the SilverLeaf VMSpc program and I could see better mpg at 62. The Dutch Star is just geared differently and takes a little more driving technique to maintain speed in the hills vs the Diplomat. The Diplomat technique, leave cruise on, manually drop to 5th about a quarter mile below the hill and relax.