I have a 04 F-150 with the 5.4 engine. When I'm in overdrive and ease on to the gas my truck rumbles a little bit when it downshifts. So, I had the plugs changed and a fuel treatment done. All done by a Ford dealership. It took ten hours and $400 and the problem is still there. They said that they checked the coils and they are all firing fine. Any other suggestions to what could be the problem?

 

Fpcm, cam phasers, PCM...there's a long list of things it could be. Start with the fpcm and see if it is corroded.

 

Any other idea?

 

Looks like I'm headed back to the dealership in the morning to try and a figure out my problem.

 

I would do a little more research before continuing to throw money at the dealer. They don't know what's going on any more than you do at this point.