Check traction motor brush springs and leads ect have had 331 on high hour trucks weak brush springs or poor connections on brush leads. When I have encountered this problem encoder counts are good , motor will run fine off the floor, but when on the floor it will code 331 under load. Do you have a sister truck available?If so swap the drive motor, only takes half an hour, if that doesn't resolve the problem at least you have eliminated the motor altogether, then swap the access 3 , it may code out for software mismatch when you do this, then go to utilities and copy setups from access 2. Again if this doesn't work you have eliminated any controller issue in a short amount of time.
In my accounts I have over 30 crown reach trucks from 5000 series to 5700 controller issues are rare.
Crown harnesses are generally pretty good as far as the controllers go, mostly plug connection issues if any, clean all connections with plastic safe contact cleaner. Sounds like you have already ruled out the encoder harness. Good luck