Lift kit

Run as fast as you can. Anything that changes the ride height from factory specs affects the driveline components, handling, and tire wear negatively. A good lawyer will convince a jury you are partially at fault for a crash when the other guy ran the red light because you have less the maximum control of the vehicle. Braking bias, front-to-rear is also affected. Reputable shops will not get involved in modifying vehicles this way because they don't want to be a party to a lawsuit. That means these are usually do-it-yourselfer projects. Do-it-yourselfers don't understand why that shortens the life of control arm bushings, or why tire wear is increased dramatically even when it is "in alignment". In my Automotive Suspension and Alignment classes, students were not allowed to modify ride height and I spent an entire class period on why proper ride height is important.

GM has a whole bunch of common problems, and a REAL lot of ways to separate you from your money after the sale. You don't need to add to the misery of owning one by buying one with even more problems put in it. I can elaborate on any of these topics if you aren't convinced.