Have you converted to mass air? You said you picked up a 70mm sensor...What size injectors is that sensor calibrated for? For a completely stock 302 ie no cam, intake, or heads, your throttle body is really too big. If you want to use that 70mm, keep in mind there are forced induction guys running 65mm tbs, I would upgrade to at least an explorer or cobra intake and then go to 24lb injectors, available on any number of mustang parts websites, ie American Muscle, 5.0 Resto, ...
88GT: Fresh 306, Speed Pro pistons, 170 TFS TW Heads, E-303 cam, 1.6 SVO RR, Wieand Stealth Intake, 670 Street Avenger Holley Carb, Full MSD, Rebuilt T-5, Taurus Fan, Hurst/Pro 5.0 Shifter, 3.73s, FRPP Aluminum Drive Shaft, BBK UD Pulleys, PA Perf. 130amp alt., BBK Ceramic LT Headers, BBK OR H-Pipe, Nitto NT555r tires.