2001 Passat Transmission

I have a 2001 Passat, 6 cylinder, 85,000 miles. Initially, my problem was shortly after start-up (about 5 minutes), there would be a "slight" clunk and my instrument cluster would all light up so PRND432 was all lit up. Once this happened, the car took off from a stop very sluggishly and it would not progress into 5th gear. Prior to it warming up, it would run fine. I took it to a VW dealer for inspection and they indicated my transmission fluid was black and that I needed a new transmission. I did NOT like that diagnosis. By shear luck, I ran into a mechanic later that day. He indicated that before spending money on the new tranny, I should have the transmission fluid drained, drive the car a few hundred miles, and then flushed. Indicating the black transmission fluid was probably interfering with the sensors. (Or something to that effect). I had the ATF replaced, with a new filter, and also had the oil changed. The car ran fine for 30 minutes UNTIL I took a left hand turn. The same thing would happen. Slight clunk, instrument cluster lit up, sluggish at the start and no 5th gear. If I restarted the ignition, it would be OK again. Driving straight, I had no problem. Making right hand turns, I have no problems. The transmission purrrrrs. Its just when I turn left! Anybody have any insight? It doesn't sound mechanical to me. More electical or something with sensors. Is my car a Republican and only turns right?