Hi and welcome to FTE!
Glad to have you here in the 3.8/4.2 forum.
Years ago there were a few guys here who went goofy doing all kinds of stuff. One even added some prototype turbo.
Things have settled down to where most guys appear to keep them pretty much stock, or maybe a few aftermarket add-ons. Nothing much as far as "real" high performance.
You just are not going to get that out of the 4.2 without a significant top-end (and maybe even bottom-end too) rebuild.
air filter / CAI
and a few other trinkets here and there.
Based on 9 years here in the 4.2 forum, and reading lots of guys experiences (including my own), none are going to give any sizeable performance gains.
Hope you stick around and join us by posting often.
my truck comes with 205 horse power and 255 ft lbs of torque ive already got a true dual exhaust with glas packs for the muffler it sounds pretty good 4 a v6 im sure yours sounds the same but i wannna get a programmer, cold air intake, and headers. thats about all i wanna do but what kind of power #s am i lookin at if i do all that