1997 Ford F250, 5.4l E4OD, 125K miles

 

Chances are it's the Transmission Range Sensor (TRS.) It's also called the MLPS. It's located on the driver's side of the trans. It's the part with the wiring harness attached.

And by the way, it is impossible to shift from 4th to OD. 4th gear IS overdrive.

 

crobarr, welcome to the forum. As Mark said, your transmission is probably shifting from 3rd to OD, if it's actually shifting. But, are you sure it's actually shifting? If the Torque Converter is continually unlocking and locking back up again, it would feel a bit like uncontrolled shifting.

When does this behavior happen? Is it on level ground at highway speeds, or is it on an uphill pull? My experience in my old 5.4L with 3 gears and overdrive was that the TC became unlocked quickly whenever the engine was under load. To be fair, though, it would also shift down to 3rd pretty quickly after that. I don't think the 5.4L engine has much torque at all below 2000 RPM.

- Jack

 

Maybe misfires? caused by weak coils or old plugs?

 

It shifts while in lockup (actually between third and fourth) The downshifts are jarring to speed up the engine, with no throttle input, and the upshifts are harsh, and speed or load doesn't matter, level ground, coasting, pulling a hill. It begins after going into lockup in third. First and second not affected. Moving away from a stoplight smooth as silk. I would think that if the TC were just unlocking, there wouldn't be the jarring feel of matching engine speed to driveline speed, like putting a manual transmission into a lower gear and "popping" the clutch, rather like just going back to fluid drive, or unlocked. Engine is in excellent tune, no misfires no hesitation.

 

OK, then I'd follow Mark's suggestion.

- Jack