Nice Z71 man. For wheels, I'd go with 17 or 18's and definately look into BFG's. Not only is it an awesome A/T tire, but they just look mean on a Z71. Also check into the whole tire package, since last I checked, BFG's were a tad expensive in 18's, but a lot cheaper in 17.
Oh, and I'd look into a custom tune (or at least a good handheld) if you don't already have one. That'll give you the most performance gains.