In all honesty before doing much of anything with that many miles on the car i would buy or crate motor or do a rebuild on your current one. The reason i say this is instead of spending money on bolt ons and then having to stop before you reach your power goals cause things start breaking or the motor can't handle what you want it to do. Save that money and put it towards a crate or rebuild. Could save you alot of headaches further on down the road. But that's just my opinion cause with that many miles I just wouldn't trust the engine.
Now with all of that said if the most has been recently rebuilt I would go with a CAI (cold air intake), TB (throttle body), and Plenum makes sure you get the flow on all these matched up so you don't end up with a bad air/fuel ratio. Match that up with a good flowing exhaust, a set of LTs (long tubes), gears and a tune...be a fun little daily driver. Then after that you can start with all the fun stuff like heads, cams...gets pretty fun.

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2002 Metallic True Blue Mustang GT
Current: K&N FIPK CAI, Pypes Violator Cat Back, MGW Shifter
Future: Whatever I have the money for...

...gotta love it when the mod bug hits
