I'd stay away from this unless you just have to have these specific mods AND you can get a General Motors Protection Plan (GMPP) warranty.
Because of the mods, it can't be offered as a Certified Pre-Owned (CPO) and it does have a lot of mods. PLUS, you can buy a brand new 2LT for less than the one you're looking at.
The same dealer offering the used, modded 1LT you're viewing is selling new 2LT's for 31k or less.
Unless you just HAVE TO HAVE those specific mods, buy new and get a new car warranty thereby saving yourself some headaches if something goes wrong with the car.