I was driving my 95 CTD yesterday and it would not shift into overdrive or lock up the converter in drive. It worked fine for the last 3 months before that it did the same thing one time. That time I tested the TPS it appeared to work correctly nice linear voltage control. The last time the problem mysteriosly fixed itself. I tried the overdrive switch to get the converter to at least lock-up in drive but it made no difference. Can someone point me in the right direction as to what controls both overdrive and converter lockup. I've tried searching the forums but havent found anyone describing the same problem I am having.

 

I have heard similar problems with relation to the brake switch on the pedal popping out of the holder and causing issues there. It acts like you have the brakes on and tells the PCM to unlock the TC...

 

Could also be the tranny temp sensor or the connector to it.
With the sensor located on the output cooler tube about a foot forward of the driver's side unplugged jump across the connector going back to the PCM with a 1000 ohm resistor from Radio Shack and see if things change.