Is it?
The Mamba will be more capable, but I doubt it would now cause heat issues (assuming same settings) - if anything the motor will have an easier time of moving the car around with a better power supply. Then again, the extra power will cause a raise in current - current = heat, so?
Is it any faster now then it was?
It would be worth also checking the throttle curves, in case you've accidently set some weird curve onto it. Also, try reducing the timing to zero, and see what affect it has on temperature. I've always run my ESCs in 1/8th scale at zero timing (for efficiency mainly), and is another way of cooling hot components down.
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