I am having a reoccurring problem with my 2011 GT. Car has no real mods except for a kn drop in filter and Roush axel back exhaust. The problem I am having is the car is way down on power and stutters above 4000 rpm. For instance launch the car and mash the throttle car will not have enough power to brake the tires loose! If you go to make a pass at 55-60 down shift into third and go wot car stutters and barely accelerates. Took 11 seconds to go from 60-80 in third gear today while at wide open throttle. Car has been into the local Ford dealer 7 times in the last year for this very issue. So far they have replaced the crank sensor, mass air sensor, coil packs and re flashed the computer ( this is everytime) Problem will seem fixed and then reappear in 6-8 weeks. Is anyone having anything like this? This is the third Mustang I have owned and Is by far the most frustrating. (Owned a 90 LX with svt Crete motor, and an 01 Cobra convert.). I am very close to setting it on fire. Please help!