Welcome to the board. 5.3 is a good choice, and becoming a fairly cheap buy anymore. When you go to get your computer reprogrammed/tuned, I suggest going thru
www.nelsonperformance.com They do great work, but if you plan on doing additional tuning, I would recommend them because they lock there computers up so no one else can steal there software. Good luck, I look forward to seeing more of this GMC. I got one myself.