2001 4.0 with 5-speed auto, which research shows is a 5r55e.

60k on the odometer, picked it up a bit over a year ago and have noticed a bucking problem at highway speeds, normally 40MPH+.

It happens both in 2wd and 4wd and 3rd or 5th gear. I tried disabling OD when it was happening and it didn't go away, that's how I know it's not just in 5th gear.

It doesn't always happen, I can go months without an incident but it seems to have picked up the last few times my wife and I were out. I'm pretty sure it's transmission related, but hell, another problem could be manifesting itself.

 

Do you have a tachometer?
Does the RPM change during bucking, this would indicate engine issue vs trans

Fuel filters are $10 and if getting dirty can cause this, causes pressure drop at the rail when fuel pump is off.

MAF sensor can also cause this but usually at lower speeds, but easy to clean, don't use carb cleaner.

 

It has a tach, but I haven't paid attention to it during the bucking. I'll do that next time.

It's do for an oil change, probably a good idea to get the fuel filter replaced anyway.

 

It happened again today, but only slightly. Traveling about 45 MPH and slight little bucking/jerking.

The tach was rock solid.

 

So you were correct, most likely a transmission issue.

There was a Ford TSB for 2000/2001 Rangers about the connector under the drivers seat.
This connector passes several system wires from inside the cab to outside the cab.
There was a problem with this connector getting water inside.
01-5-2
On this list
https://www.ranger-forums.com/genera...d-ranger-6485/

This could cause transmission issues, speedo issues, ABS issues, ect.....

 

Thanks, I just read through the list, the TSB listed a bunch of OBD codes that I'm not getting, but I'll check the connector out.

I was really hoping it was a common issue and I'd have 10 people post and point out what it is, lol. I've ran in a lot of Mustang circles and some vehicles just have their common problems. This apparently isn't one of them, shame too because it doesn't happen often enough to get a mechanic to see what the problem is.

 

could be a transfer case issue to the motor to move it in and out of 4wd has been none to fail and it may not be fully going into/out of 4wd so every so often the gears can catch making it buck could be totally off on that one but its worth checking.