Drift;

Double check the motor wires just inside the can where they connect to the windings. You may have to look real hard, but see if there is any fraying or if a few of the strands are broken. If you don't secure the motor wires very tightly so there is zero movement, the vibrations can cause a few of the strands to break at the base of the winding. only a couple of broken strands can cause the motor to overheat and eventually it will just smoke itself. it is not something that you can easily see with the naked eye, but I have had this happen on a cuople of my Neu motors until I figured out I wasn't securing the wires tight enough.

See how I have the motor wires basically ziptied solid to the chassis brace?