Auto 944 Trouble in reverse

[Fetty91]

Hello, I have an 84 944 AUTOMATIC that is having trouble in reverse. It works well in all forward gears, but shudders in reverse and moves very little if the pedal is pushed more than an infinitesimal bit. I did put some Lucas stop slip in it, but I was having similar issues to begin with.

This is my third transmission in the car. I installed this newly purchased transmission myself, and followed instructions to the letter. I drove my car about two miles on a test drive and to let the fluids level out, making sure to test every gear (including reverse). Everything worked perfectly. Upon getting back, I tried reverse gear again, only to have the car barely make it up my driveway. At that point, fluid levels were slightly too high, but I hadn't done anything to really stress the transmission on the 2 mile drive. After a couple days of sitting the car started up and drove in all gears just fine. I pulled it into the garage, drained the extra fluid and put in some Lucas transmission repair. When I started the car up again, it still went in reverse correctly, and the car went forward just fine as well. All gears worked correctly for about a mile and a half. I tried reverse again and I was rewarded with an awful shudder which reverberated through the whole car. If I accelerate backward very slowly, this doesn't happen. If I press the gas pedal too far past the shudder, it just revs the engine and the car acts as if in neutral. I'm guessing that this is a problem with the friction plates, but do not know for sure. Could this be a bad torque converter? What would be the difficulty in replacing a friction plate if I am mechanically inclined and have a workshop manual?

Please do not tell me that this is an issue with the shift linkage. I already know this to not be the case. I have checked and double checked it.