The past couple weeks the torque converter has been unlocking at highway speeds, only when it's hot. If I used the lockup switch it would stay locked.

On the way home today it dropped out of overdrive, a few times it shifted back into overdrive but shortly after, back out.

It does have the following codes:
37 Torque converter clutch (TCC) solenoid/ transmission fluid temperature (TFT) sensor
45 Overdrive solenoid Wiring open circuit/short circuit

12 Engine control module (ECM) -supply voltage disconnected within last 50 ignition switch ON-OFF cycles
47 Alternator -voltage low

Is it possible that replacing the torque converter clutch solenoid, transmission fluid temperature sensor and overdrive solenoid would fix this? Or is it more likely that it has more significant issues?

It's a diesel. Not sure what transmission it has, the book I have says it's a 37RH, but it's a 4 speed not 3.

 

fluid temp sensors is probably your root cause, the trans will drop over drive if too hot, possibly lock up? I'm not as familiar with the RH series and their computer logic, or lack there of

 

On the 94, the sensor is external. Should be screwed in a schrader type valve on the line at the front of the trans, very close to the trans. I think only trucks that got the heavy duty package got the sensor....... Most don't have it.

It's also entirely possible that the trans is indeed getting hot.... Do you still have the check valve in the cooler line just in front of the engine???

 

I did not see the check valve, a previous owner may have removed it. I'll order a temperature sensor and see if that fixes it.

 

Make sure you even HAVE one before spending money.

 

I did verify that I had one before ordering the part. Replacing it seems to have fixed the issue. Thanks.

 

Gotta love the easy ones.