I was GT shopping last year as well. I suggest looking everywhere that you know of, ie, autotrader, cars.com, in newspapers, and at local dealerships. Well kept GTs are out there, you just gotta look for them. I found a bunch of Gts, from 1998 to 2004 that I was interested in ranging from stock to decently modded, low miles to high. I suggest comparing the price, year, miles, mods, condition, etc. and see whats feasible for you to buy. Then most importantly test drive them!!!

I test drove 3 different Gts and they all felt completely different. I went with mine only after the test drive because it felt the best. Been very happy with it ever since with no major issues. Hope this advice helps and you can have as much luck and fun as I am having

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2003 Mustang GT, Green Performance Air Filter with stock tubing and air box, Ford Racing 70mm Throttle Body, C&L Trueflow Upper Intake Plenum, Pypes Violator cat back, 3.73 gears, Diablosport Predator Tuner, Tri-ax Shifter, Steeda UDP's, Mach 1 chin spoiler, Mach 1 grille delete, H&R lowering springs, Simco Gauge Cluster, Bullitt pedals