I had a 2001 5.9 HO, after the warranty was done I put the following on it.
Fresh air intake box (Air Aid).
4 inch free flow mandrel bend exhaust.(delete catalletic).
Super chips set at heavy trailer tow.
It dinoed at the rear wheels at 450hp & 850 Tq.
unfortunately the clutch was the weak link and had to replace with one that could take 900 Tq.
gained 3 mpg mileage, and towed my 12,000lbs 5th wheel RV or my 4,000 Lbs truck camper like nothing. When I towed my 4,000 lbs boat I did not even know it was behind me.
I put 515,000 on it and never had any issues, best truck I ever owned.
I put it up for sale at 10:30 at night after trying to fine some for sale, only found 3 and all were in very bad condition, from need transmissions to motor needs overhauling. They were priced between $9 - 10k.
I put mine up for $12k and had 6 people the next morning at my door wanting to buy the truck (I sold it to the first person).
Lesson learned the cummins Ram is holds its value, I could have gotten at least $20k for it. I owned the truck for 12 years, sold it in 2014.
I only paid $26k for it when it was 6 months old with 15,000 on it, from a ford dealer the original owned decided he wanted a Ford instead (big mistake on his part).
Note: truck before was a 1992 3/4 ton Cummins I put over 500,000 on but also 3 rear diffs, 2 tramissions, front end completely redone, and numerous universal joints. And very badly rusted out.
It only had 160hp & 400tq.