Most suggestions here will help but almost all at the upper-end of the RPM range. Throttle Body, CIA, Muffler, etc. I agree that these trucks are sorely lacking in low-end punch and I am sure they are tuned for highway mileage. I don't care as much about going 130+ mph as much as I do about getting from light-to-light or onto the freeway itself. My 3500 dually cummins (8500#'s+ empty) Ram can take my Hemi (4 tires and several thousand pounds less) from light to light any day of the week. Of course once the Hemi finally winds up it's great, but by that time it's over. Plus I tow with both my rigs and low-end is where it's at on that front as well. I have 3.92 rear-end and would have opted for 4.56's if I had been given the choice. The tranny (torque conv) and gears eat up a lot of this engines potential at the low-end and actually kill low speed mileage as a result. A tuner could help some but gears are your only hope if you want near invisible warranty issues and the ability to keep those nice 20" rims.
2016 3500 Laramie MC: Bilstein 5100's up front, 20" Fuel rims with 275/65-20 Micheline LTX MS/2 tires, Weathertec Floor mats, 45 gal RDS tank, Hensley TS3 hitch, Billet DEF and Diesel caps, DeeZee tailgate assist, Bull Ring retractable stake pockets, Amp Research steps, hybrid window tint.