So, I recently noticed I’m having issues with my overdrive while hauling. It’s a 1998 F150 with around 180-190k miles on the engine. Initially I had to get a new overdrive switch as the one on my truck was missing the button at the end of the shifter. Replaced that and when I turn OD off, the light comes on that it is off. I also checked it driving down the road without hauling. Going about 45-50mph turned overdrive off and it downshifted as it should. But when I tried hauling my bumper pull horse trailer with one horse in it, it gave some issues. There was a hill I had to climb just past a light so I was just starting out and I had overdrive off, everything seemed to be working okay and then for some reason mid hill my truck decided to shift up a gear. So naturally it plummeted under 1k RPMs and sounded like it was going to stall out so I shifted it into 2nd to get up the hill and back into drive once I cleared the hill. Once I got up some speed I didn’t notice anymore issues. I recently had some issues with this same truck, I have a couple bad coil packs and a bad starter plug, got those replaced and then it started doing this. I notice no issues with the truck without hauling. Any recommendations? The only shop I called said they wouldn’t be able to diagnose unless I dropped off my truck with the trailer attached. But I’m needing to use both my truck and more specifically my trailer to haul a horse a good distance and I’m trying to avoid having to do that. Thanks in advance!

 

What engine do you have, and is the transmission a 4R70W or E4OD? Has the OD OFF light ever flashed? If so, read out the transmission codes through the OBD2 port.

 

Should not be towing with overdrive. That will burn up an auto tranny. Very quickly.

 

If you get going fast enough with the trailer to allow upshifting to OD, the TPS will take it back down as soon as you put more throttle than the engine has torque enough to pull in OD.
You need to know that OD changes the final gear ratio by about .70
If your rear ratio is a 3:55, 3:55 x .7 = a final ratio of 2.49 rounded up.
You can't expect the small motor to produce enough torque below 3000 rpm to pull a truck and a trailer that weighs upward of 10,000 lbs. up a hill without down shifting.
It's all set up in the PCM program to down shift by intent the same as you would driving with a manual shift in the same truck.
This is why these truck are not used with manual shift for towing heavy loads because the transmissions available are not very strong.
Good luck.