like rxbpy said when you are driving and using part throttle mostly, you are using the electronic resistor part of the esc (transistors) which will get rather warm no matter which esc you use unless you use one with a fan on it. They do make a small fan that will help that, there are several that would work.

If when you were using the Duratrax Intellispeed 12t esc and it did not get so hot it thermalled..... got hot and quit till it cooled off..... you should be fine cause the motor is not hot and the batteries are not hot which say you are not using very much of a draw on the batteries.

Just be sure all connections at battery, esc and motor are good connections and are not getting hot and causing high resistance which would cause the same problem. But I think it is from running slow.

Thanks
Dudelive