Need 545RFE Help

Had a similar problem with my 95 dodge 2500 with cummins

Convertor would lock and unlock at highway speed

I would slow down some and it would stay locked in

Started with having the Trans rebuilt and new convertor at 97,000 miles, didn't change a thing

I changed the Throttle Position sensor, and seemed to help for short term, then started again

At the time I would run 72-74 mph on interstate, once I slowed down to 68 would stay locked in. Then more checking and then it started to unlock at 68, on the last trip before we got it fixed I could only run 65.

Installed a switch to keep the convertor locked in then the transmission temp light started coming on.

So the transmission temp sensor was changed and cured the problem

Not saying that is your problem, but it was a $27 part and I chased the problem for over 6 years ( don't drive the truck on the road much)

Suspected parts would be the TPS, loose connection, bad ground or bad temp sensor

Hope it doesn't take you 6 years to find it..... LOL