It's possible that your servos are drawing too much current for the BEC of your ESC. According to the ESC specs, the maximum burst current for that ESC's BEC (the circuit that provides power to the receiver and servos) is 3A. That means that the continuous current is probably much lower. Drawing current close to the limit will most likely overheat the ESC. You can check that the end points of your servos are properly set, meaning that you have to make sure that the servos are not trying to go further than what they are trying to move allows, If they bind, they will draw lots of current.

Martin Paradis