I hope you are making headway finding the source of things. I agree that checking the ODB codes is the first step. With a little luck the car will tell you what is wrong. I attach the instructions on how to check the codes, below.

What area do you live in? If you post the general area, the brickboard members can post local Volvo bone yards you can check.

Good luck and post what codes, if any, you find.



On-Board Diagnostic Codes for AW-30-40 Series Automatic Transmissions.

These electronically-controlled transmissions also contain a diagnostic code series that you can access easily from the engine DLC module (the same one as used for the ignition and fuel injection codes.) Note that this Mode 1 procedure for code retrieval works only for OBD-I (pre-1996) 960 cars.

1. Open DLC, (Diagnostic Link Connector) insert Test lead into hole #1.
2. KEY IN position 2, engine NOT running.
3. Push and hold DLC button for >1second, but, 5sec. release, wait for LED to light, then hold button for >5 sec again. And you are cleared.
There is also a self-test mode 3 you can enter which is a two man job. One enters the code through the DLC and the other guy is under the car feeling for each solenoid and other device to activate in sequence. Then, you can run through all the gear positions and modes and the DLC will respond with a code that