i had problems with my COP on my 5.4L Expy. Problem would not show up except for hard accel or at highway speeds and trying to pass so mashing the gas. COP was not completely bad so the Ford tech did not find it until they data logged the truck with me driving as I normally do.

By the way, once that COP went bad..the rest soon followed afterwards....

 

Go thru the ignition item by item. There's a TSB on the plugs so be sure, if you have the dealer pull them, that they're aware of it. If it isn't ignition, then I'd begin looking at fuel delivery. Maybe it's time for that GT500 fuel pump!

 

the problem was spark plugs! replaced them today and all is good!