its not the transmission itself. If it were it would not move. What it sounds like is a connection problem from the TCM with the valve body solenoids in the case. This is a dealer specific item I think you should address because it can be anything from :
1. failed TCM
2. bad ground
3. faulty wiring harness
4. solenoid control problem
5. Any or all of the above.
The thing is the dealer has the interface tool to activate all the solenoids in the trans. using the laptop and test in/outputs on the TCM plus other Powertrain codes and check for ground circuit resistance and all. Or it could be a software glitch which the dealer could reprogram or flash the memory.
Without seeing the car but seeing the high mileage I d say maybe a bad PROM chip in the TCM.
So make an appointment and pay the diag. fee to get an idea what what.