MP,
Maybe I missed some stuff but is this a 5.3 or a 6.0 truck. I would try to find a set of used heads and a LS1 cam to throw at that sucker plus an exhaust to make it sound good. Make sure if you lift it to find a nice tire that is off road capable but not a hell of alot of road noise. Try to get a yukon denali front grill for it too. If you really would like to go extreme contact Texas Speed and Sound and get there MS4 cam.
Good luck with the truck,
Rev440