04 f150 xlt 4x4 5.4l has had a miss under load, replaced plugs and cops . Problem went away,3000 miles later it's back. Replaced plugs again was firing down the insolator . Problem gone again , but loss of power. It runs fine just does not have the power I think it should. I just replaced the alt , was over charging the battery. Have had problems with since day one, to the point ford replaced the motor under warranty . Now at 89,000 problems again . The only thing I can think of is the computer needs reflashed. You can disconnect anything and it will not set off a code. I have know idea

 

Did you use motorcraft plugs?

 

Yes only fomoco parts