Code P1820 hard shift/A/T shifting out of gear

[ftmfg]

Hello Everyone, Hoping someone can help,this has really got me stumped! My truck is a 1996 F350 4x4 PSD auto. E40D fresh air intake, and 4" straight exhaust with 207K.Did have a defuser 18-K Power Module for a while has been removed. The trans. was supposedly replaced at around 170K. Here's my problem(s) code P1820 keeps coming up when the check engine light is on, the trans. shifts hard (been told it may be the torque converter locking up) when the check engine light is off the truck shifts normally. The trans. will not stay in a higher gear(keeps shifting in and out of 3rd and OD) does not appear to be slipping. Also recently noticed that the cruise control is not working(related?) The engine runs strong and I'm thinking the P1280 code is a red herring and has nothing to do with above mentioned problems. Bad PCM/ECM (computer)? Bad torque converter? I've had this truck to shops all over town and even bought a Superchips 1705 after paying one shop the cost of the 1705 to tell me what codes were tripped but couldn't tell what was causing the shifting problem. Please help. I love my truck and want it back to ehere it was before all these problems.
Thanks for any help!

[ftmfg]

Does anyone know about these, TransCommand® for 94-97 Ford E4OD or 4R100 Automatic Transmissions
Thanks

[bigcountrysg]

You need to take the truck to a Transmission Shop. Shifting in and out of OD and 3rd, hard shifting is not from the tc locking up. There is something wrong here. A trans command will not correct the problem at this point it will be money down the toilet.