I'm new to this forum, but have already been helped by several members after my first post. I have a 2001 quadcab 3500 2wd, high output 5.9L 24v. Mostly stock except for 300hp injectors, Fass system, airbag front suspension, 100gal fuel tank/toolbox in the bed, gear vendor overdrive with the 6sp manual, still with the original clutch. It has 19.5 inch 12 plies on alcoa rims. Interior is nice with leather power buckets , and i have put on an aftermarket dash cover after the original started the dreaded cracking. It has heavy duty ranchhand grillguard and rear bumper, with a concealed fifth wheel hitch and receiver in the rear bumper. I also installed dynamic balancing discs on the front wheels. They are well worth the money. Lastly a 4" exhaust . Most all of the mods were done by the original owner. I replaced a valve in the gear vendor..its great(I turn 1900 rpm @ 70mph, and average right at 20 mpg if I keep my foot out of the turbo). Best mpg = 22mpg.. Thank you to the fellas who answered my first query with easy to try mods.