Ok, so I'm new to the mustang world, just got mine this summer. So far the only thing i have done is a CAI. Now I'm confused and don't know what to do next. My car is an 03 GT, Would it be best to get a catback (someones offering to put one in for 300), or some 4.10 gears (I have a mechanic friend who will help put them in, not sure how much he will charge). just wanted some other opinions. also, is a 3" catback worth it, or should i just go with mufflers for now?