Ok-- a few things to do to make it into the 400 hp club on a NA 5.3L:

Flat top pistons. (get some from a NBS 4.8L truck)
Stage 2.5 heads with a lil bigger valves. (2.02" intake/1.575" exhaust)
TBSS intake with 90mm TB.
Cam size is fine.
All other supporting mods.
4.30 gears.
3600 stall.
Caltracs.