Having major tranny problem. Coming back from Florida my rear wheels seemed to try and lock up if I let off the accelerator the slightest bit. Wasn't sure at first what the problem was until it kept locking the back wheels over and over again and releasing. The tranny started not shifting right and downshifting on its own. Finally after rear wheels locked completely on wet road and loosing control of my truck I pulled over and had it towed to Va. Took truck into Ammco where they did a complete rebuild of my tranny with all up graded parts and new billet torque converter. Reverse clutches were fried and some metal parts welded to some other parts. Reverse solenoid was replaced and was told that showed up faulty on their code check. Got tranny back in truck and on test drive rear wheels again tried to lock up. Was determined that the ECU was faulty and telling the tranny to go into reverse. Ford dealership ordered new ECU unit and installed and downloaded all stock settings. After this I had to hook my X4 SCT tuner up to the new ECU and down load my tune file from National Speed for the truck and super charger to perform properly. Took truck out for another text drive and rear wheels still tried to lock up when I would let off the accelerator. Then as we kept driving tranny would not shift in to 5th gear stayed in forth at 50 mph then for no reason downshifted to 3rd RPMs went to 4000 and then nothing. No noise no anything. Transmission wouldnt respond to any gear what so ever. The mechanic that was riding with me had his computer hooked up to read any faulty codes said the computer was saying the truck was in Park no matter what gear we shifted to. They are scratching their heads. Any ideas here. Been without my truck now for 5 weeks and this is getting old. Thanks Bill Munden here new member.

 

Does this trans have an MLPS on the side of the case? I know most Ford trans have a special box that connects to your shifter, it tells the computer (thru a voltage drop) what gear you are in. The computer thought the truck is in park, that would wreak havoc. They can monitor the MLPS pid and voltage. Real cheap fix, was a failure point on some trans.

They also talk about a ground strap here:
https://www.transtar1.com/TD-July-2017

I think you have that trans, correct me if im wrong.