TC,
It sounds like your problem may be in the transmission ECU. If the Trans Check indicator stays on, the ECU has detected an error and stores the code. If there's no code, the ECU may be at fault. Be sure the tech is using the correct procedure to read the codes at the keypad. Press the up and down arrows together twice to access the codes. (Once will display oil info). Use the mode button to scroll through the codes. If the Mode button is pressed for 10 sec it will clear the codes. Also,have the tech check the cable connections at the transmission. Due to the environment they are subjected to, they can give one problems with faulty connections.
Steve