Well, I'm not up on third gens, but your car only has an intake. At your level your exhaust does almost nothing but make the car sound better. The only exception to that is if you got rid of the factory downpipe with the hideous u-bend on it and the cat. If you still have the factory downpipe and u-bend, your car is probably going to run a 14.5 or 14.6 1/4, if you don't spin, have traction control off, good launch in general, etc.
IF you want, I'll race your pops and put him in his place about GTP's!
(FYI, my car should be running about 13.8 right now)
Edit: Let me clarify. Exhaust work is always good. But from the cat back, these exhausts don't start holding you back until the low 13-second 1/4 pass area. You will however pick up a tenth or two from getting rid of that stock downpipe.
Edit2:
P.S. Consider yourself lucky. My father vs. son battle has a TrailBlazer SS on his end of the deal >
