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.

 

Slip Yoke bump? I"ve had to lube mine several times throughout the years and it always feels like a trans problem. Not saying thats it but...

 

My brothers 12th gen had a problem like this and the yoke was replaced but nothing changed. The truck has 35" tires and needed trac bars. The skip we felt was axle wrap.

 

Have you changed the spark plugs? That sensation of a sort of misfire or bucking at 40-50mph under light acceleration is indicative that you need to change the spark plugs. These engine like to do weird things when parts need replacing.

 

Could also be the infamous OD clip that breaks on the 4r75

 

My 2005 has a similar issue. It's really random and doesn't happen a lot. Feels like a slip at low rpm when accelerating. Had the transmission serviced and still happens. It's been bothering me and no one seems to know what it is.

 

There's some videos on YouTube on what I mentioned earlier. Changing spark plugs fixes it. Has nothing to do with the transmission.

 

Agreed. When I had what I thought was a transmission issue new spark plugs fixed it.