Your going to have Issues. The previous Owner should have set it back to Stock. Your going to be stepping in the Dark, because you don't know what was done to the Car as far as Tunning. Try to find a nearby Performance Shop who have knowledge on Tunes and Tunning, see if they can figure out what was done to it and if it still have the Tune changed in it. Also if they can Custom Tune it. If it was set back to Stock, then you will be starting from scratch, sort of. I hear the X4s are good, mine is the X3.
07 GT SCT: CUSTOM TUNE by "MUSTANG SPECIALTIES". STEEDA: CARBON FIBER HIGHFLOW CAI. STEEDA: 1 PIECE ALUMINUM DRIVESHAFT. FRPP: 4.10 GEARS. MAGNAFLOW: AGGRESSIVE 3" 409 STAINLESS STEEL DUAL EXHAUST. BBK: LT 304 STAINLESS STEEL HEADERS, BBK: o/r X-PIPE. MSD: BLASTER PERFORMANCE COIL PACKS. POWERSTOP: CROSS DRILLED SLOTTED ROTORS. WHEELS: STAGGERED WHL 22X8.5F-22X10R.