Just bought this truck from my neighbor. 58,000 miles on a 8 year old truck. It is box stock and clean. I cleaned it up even more. I have never owned a diesel before or a GMC. This diesel is Awesome! GMC has a slightly better finish than the Silverado I sold. We tow a 33ft Keystone Ultra lite camper that's 6,800lbs like a dream. There all expensive and I don't know why the comman man would spend the money on a new one. Enjoy shopping and go clean used. Some mods in the future, good deals out there on used perf. parts
Duramax/Allison is just Awesome! Can't imagine needing anything bigger. The Allison Trans is great going up or down hills. This is a dream ride with our camper behind it. My wife loves the ride. Heated leather seats, Bose stereo. First class in a 2005 SLT 2500 HD Duramax. Clean older trucks never die, they just get more attention.
Duramax/Allison is fine box stock.
This is what I will be considering: mild tuner, high flow air filter in stock box, LBZ turbo inlet tube, 4 inch exhaust, sulastic shackles to smooth bumps. (No hurry on any of this)
This truck is a true performer with just a few minor (cheap) add ons that won't hurt the truck.