I have an '08 V6 automatic. The first mod I want to make is a dual exhaust. What size pipe should I go with? There's a Pypes catback kit on Americanmuscle.com that's 2.5". Would that work okay? also, that's not something that would require a tuner is it?
2.5" is the factory diameter of GT exhaust so that is a good size. No it does not require a tune. Check to see what that is made of, Pypes stuff is made in China so if its galvanized steal you'll be buying it again after a year or so. You can look around eBay or Craigs to see if anybody is unloading stock GT pipes and mufflers they will bolt right up just may need to buy some rubber hangers.
Good ones are made of stainless steal. Yes GT pipes will fit as you can see in FRPP dual exhaust kit M-5230-V6 this kit is basically the FRPP X pipe, mid pipes and axle back mufflers from a 05-09 GT, it also comes with hangers and I believe a template to cut the bumper.
Stock GT bumpers should be available cheap also: check new takeoff parts website, brenspeed, and others. Anyone that has put a body kit on has to get rid of the stocker, or you could go with a body kit yourself.