I have an 08 F150 5.4 4-speed auto 4x4 with 3.55 gears and 135k miles on it. A while back it started making a "skip" from somewhere in the drivetrain in which the engine wasn't hiccupping but it felt something like if a chain and sprocket or a mechanical gear was skipping a tooth kind of thud. It has gotten worse lately and I'm trying to figure out what it is as it only does this in Overdrive at low RPM and usually only going up a grade. Rear end fluid was changed 40k ago, tranny fluid 20k ago, transfer case and front end fluid less than 1k ago and there were no shavings in any of the fluid changes. The truck also has 33" tires and a 2.5" lift. Any help would be appreciated.

 

they tranny may not be the issue the motor may need a tune up

 

Mild misfire, usually.

 

Yeah, this "skipping" or "hiccuping" from the 5.4L V8 under light acceleration in OD on flat roads or up a grade means the engine needs new spark plugs. Should have been doing this between 80,000 and 100,000 miles on these trucks.

 

not always. it varies from truck to truck

 

Maybe so, but my search (which also involved watching some YouTube videos) showed that the consensus was the spark plugs.