Headers are a must if you can get away with them in your state. Not only do they look great in the engine compartment, but they sound awesome. Easy to install on the GT too. Get them Jet Hot coated.
I've been told they aren't worth much power unless you're over 650whp? Also does the heat deteriorate other things in the engine bay?
I've got an air back squeak that is driving me crazy, is there a trusted source to fix this stuff in DFW? When you apply pressure to the air bag cover it goes away.