Try performancetrucks.net , thats where I started out at(even have a green name), you wont find a better place for GM truck performance. Ill start by asking how much his budget is first?
Heres what he should do in this order bang for the buck wise:
tune(custom no handheld Wheatley or Nelson do a good job also blackbear uses EFI and is a little easier to get ahold of), K&N drop in filter, cut out the front of the airbox(CAIs arent worth the money), lt headers/ditch the cats(if possible), exhaust(magnaflow or corsa my personal favorites).
That should get him started, if hes willing to drop the transmission or crack open the motor we can talk further, thats where the real fun starts.:cool2: