Overheating problems on LSP

I can get the MM esc to thermal after a few minutes. I have a LSP with a 8XL, running on 4S trakpower 4900, with 16/46 gearing. No fan, but I have a RCM heatsink on the motor, which stays cool enough to hold onto even after hard running. The batteries do not even feel warm. My MM gets smoking hot. I am going to put in a 14t pinion and add a fan. There is no binding in the drivetrain, as it rolls freely. I have all the controls on the MM on their lowest possible settings. The MM rings and the car stops when this happens, I assume it is thermalling.

If I can only go a little while with this setup, will the smaller pinion and fan help much? Is it possible the batteries put out too much power for the esc?