Some history.... I have a 1998 F-150 with the 5.4L. About a year ago,I blew a spark plug outta the head, drilled and tapped the head and put a heli coil in. So, every time I replace the plug, I have to replace the heli coil as well.
Current problem... My truck every now and again will stutter when I am driving it. I thought it was the spark & heli, so I replaced them. OK, not the problem. It happens when I am running up my RPM's around 2500, or when I am going down a hill, when it kicks it will sometimes bucks 3-4 times. My RPM's though, they do not move when such is happening, so I conclude it isnt a tranny problem.
Is it anything to do with the overdrive? Tries to kick into overdrive, but cant??
Is this by any chance the passenger side rear spark plug that you are constantly changing? The coil pack related to that location is notorious for failing. My buddy has same truck and I have replaced that coil pack 3 times in 2 years. His acted the same, it would only miss at certain RPM ranges, where usually ignition problems effect the entire operating range