Mekanik

While I do not have a diesel, I can tell you I installed the AMP power steps off my old 2011 GMC Sierra 1500 onto my 2017 Sierra 2500HD Gas no problem at all. Ran the wires into the door panels and hooked the triggers up to the door lock/latch wiring and they've been working for 5+ years. I have installed AMP power steps on diesels in the 14-19 year range, again without issue. The only thing that's different as far as I know is the right front step mount/pivot. It's different to clear the DEF tank obviously.

I bought a high country grille from the dealer cheaper than the ltz/z71 grille my truck was supposed to have

To which I agree on older models. However, 2010-up has a seperate tcm that is a part of the valvebody INSIDE the transmission that your average joe cant just swap out lickity split!

Having been a general motors technician and a tuner on the side, I can tell you first hand that GM CAN tell if the vehicle has been tuned or not and how many times the ECM has been flashed if they in fact want to know. The average tech at your dealership may not know how, but GM as a corporation can! No matter what anyone says. I've seen it firsthand. Hell, they can even check calibration files through OnStar now!