I have the same issue. Been chasing it awhile as it was intermittent. Finally caught it on the scanner. It loses input shaft speed. Then goes into limp. Either sticks in 1st gear and is speed limited to about 3000 rpm. Or defaults to a higher gear and stays there. The speed sensor is internal above the valve body. It comes as part of the solenoid plate. I found one for $140 on line. Haven't had a chance to swap it yet. Another week or two.
Doug