Four years ago I purchased a 1939 Dodge pickup model TC.
The seller started the project and never finished it.
I was told it was 80% done. What I wasn't told it had 80% left to go.

Here is the deal. The truck has a 5.2 Magnum engine (completely stock) from a 1994 Dakota. It has a 1983 727 Torqueflite transmission.

For obvious reasons, this is a total mismatch. The 5.2 is computer controlled, and the transmission is hydraulic. I was assuming based on the 1994 model year engine that this is an OBD-1 system that only controlled the engine diagnostics, and not the transmission.

Well guess what? I have two codes showing on an OBD-1 scanner.
The codes are open, or short, in the overdrive solenoid relay, and open or short in the torque converter lockup relay. Apparently the computer is trying to analyze systems that do not exist on the 727.

Having said all of the above, here is my only real issue. I can run the truck up to 60 mph and it will run all day long real well. However when coasting down through the 45 mph range, the engine shuts down. Not every once in a while, but every single time.

Now, I can go to neutral and restart the engine, and as long as I stay under 45 mph, the truck runs good. But when you take it back up to 60 mph and then coast down to the 45 mph range, it shuts the engine off.

I am at a loss to even try to figure this problem out.(other than change the transmission and get one from a 1994 Dakota and get it wired into the computer).

BTW..The 727 transmission does a speed sensor solely for the VDO electronic speedometer. There is no other electrical wiring on this transmission. The speed sensor, which came with the speedometer is wired to the speedometer, and nothing else.

Does anyone have any ideas to overcome this mismatch to where the truck will coast down past the 45 mph range without shutting the engine off?

Thanks