Like DaveS says, these newer engines have some power hidden in the programming, and keeping it street legal for you or the next owner (if that's a concern to you) is more involved than on older stuff. Have you been on the vehicle specific forums to see what's been done by other owners? Here's one link that seems to have five or six pages of owner interaction for a starting point. If you're looking at getting more into it post your details. Link - Squeezing Performance out of the 5.3L Page1 - GM Forums at GM High-Tech Performance Magazine