I was on my way to work today and when i pulled out of the driveway my GT started loping very slow and hard. It was shaking the whole car kind of like a large cam would but i had very little throttle response. I turned the car off and back on and the idle and response was fine and the car got me to work fine, but i am worried as to what it is. I am clueless as to if its a fuel problem or spark plugs, ignition, etc. No check engine light came on. 2008 Mustang GT Premium 4.6L Stock except for K&N Air Filter, Flowmaster axleback's, and Ford Racing 2" drop springs. Any advice is appreciated, Thank you.