I too have been battling this problem for a long time. I even had my trans rebuilt and everything replaced, including the TSS and VSS. The problem was still there. When the O/D light would start blinking I would pull off of the road and restart the car, no more blinking light but a hard 1-2 shift that would last only a short time then go away until the light would blink again. Well, the last time I changed engine oil my car wouldn't start. It turned out to be a bad crankshart sensor. But, since I replaced the sensor my trans problem hasn't happened {2-3 weeks}. THE ONLY THING REPLACED WAS THE CRANK SENSOR! So, I must conclude that the PCM uses the crank sensor when calculating slip for TCC sol. control. I know there are other sensors that are used for this but didn't know this was one of them. If I hadn't cured the problem accidentally I would still have it. I hope my past experience can help you or possible find a new direction to look.
