P1246 is not a gearbox problem. That code refers to the generator.

P1746
The Diagnostic Trouble Code (DTC) will set when with the engine running in gear at cruise speed and the Powertrain Control Module (PCM) detects that the Torque Converter Clutch (TCC) circuit was shorted to ground.

The P0731 code occurs when the PCM detects a discrepancy between the speeds of first gear's input RPM sensor and transmission output RPM sensor. As a result, the vehicle cannot shift into first gear, and it could indicate that the transmission is slipping.
P0732 is similar to P0731 except this is for second gear.

P0771 - Shift Solenoid E Performance / Stuck Off

I am not convinced that the Automatic Transmission Control Module is faulty. Who will pay for the Automatic Transmission Control Module when it is not the cure?
Besides fitting a new one, electronic control modules can be repaired - maybe not in all cases, but I would try that first if the ATM is really faulty (which is a big IF in my opinion).