The mamba max has a lot of programming options. You may have to go through it and make sure some parameter is not set wrong, like operating on sensored with a sensorless system. I assume you are using the mamba motor with the MM ESC? That is a sensorless motor and it will cog at low RPM. Make sure your gear mesh is not too tight and your transmission spins free. If there is any binding, it could be enough to stall the system, although at full throttle, it should still shoot out of the box. I don't know what else to tell you to try. Good luck.