[351wStang]

If its only running rough at higher speeds it could be any number of things...but are you sure its under the hood? It could be suspension. How are your tires? When was the last time you had it aligned? Does it vibrate when braking? If it is mechanical then i would check to make sure you are getting good fire. Then start worrying about fuel. O, is this happening under wide open throttle or normal acceleration? Try some lucas or techron before you start spending the big bucks.