I've got an 07 GT w/ 5 spd manual, and cold air intake, should I get a tuner or exhaust first. Just wonder which one I should get first. Thanks for the help!

 

Tuner for sure.

Cat backs dont add squat for power, especially compared to the $$$ per HP (and $$$ per smiles) that a good tuner provides

 

thanks, what tuner would you recommend, cuz i am going to get new exhaust with an h-pipe and also cuz its not loud enough for me.

 

Well, I may be a bit biased, but IMO the Trinity is the coolest tuner on the market for the Mustang.
Check out the Trinity

If you are not looking for a monitor device, check out the inTune, its a simple plug and play device with a full color touch screen, and will do what you are looking for.
Check out the inTune

Thanks