Have any engine codes? Or any engine mods? There's just so much to look out for...
I remember when I first got my GT and it had that restrictive stock airbox, the car would become jerky at high rpm because it just couldn't suck in enough air through the factory intake. I put in a small cheap aftermarket cai (I didn't even have a tune at the time) and the car breathed so much easier at higher rpms.
But it could be anything though...
2008 Windveil Blue Manual GT. BAMA 91 Performance Tune. LED Starter Button, Retro Shift Knob, SLP Loudmouth Exhaust, Ebay CAI LOL, MMD Quarter Window Louvers, Roush Rear Spoiler, Raxiom Gen5 Taillights, LED Third Brake light, MMD Hood Louvers, MRT Rear window louvers, Exedy Stage 2 Clutch, Exedy Lightweight Flywheel, SR Performance Stainless Steel Braided Clutch Line, Dot 5.1 brake fluid ftw, JLT Oil Separator, SR Performance Strut Tower Brace, SR Performance Rear Shock Tower Brace, Triton V3 Switchback turnsignals... etc etc