I have a 99 f-150 supercab, 4X4, 4.6, auto. It has been what seems to be missing for a split second mostly under a load a slower RPM's. but somtimes when It is revved out it has done it. A fuel filter has reduced it significantly, but still is there some times. I want it to run like it should. The dealer isn't much help. I have 60,000 on it. Any help?