California generally doesn't approve any exhaust mods. The K&N is IMO the best intake you can buy.

 

as mentioned k and n, will satisfy your noise maker needs, car will sound better, and have moddest HP hain,s $300 ish shipped from amazon, and if you have a socket set, installs in under an hour.

highly recomend you get a shift kit for your auto, no engine gains, put you'll notice the faster shifts. i dont have a link handy, but im fairly certain they are cheap

EDIT

http://www.racingsolution.com/chevy/...tplus-kit.html

its easy to install if you are comfortable doing basic wiring, (stripping, cutting + tape, or optional soldering etc.)