Most probably nothing to do with 2S battery since your ESC has some sort of built in BEC which regulates the supply voltage to the receiver, usually 6V typical

If you are doing a lot of sawing action with your steering or the servo isnt rated for the application, the motor inside the servo will easily heat up and possibly overheat. Seeing you are running a stadium truck, the servo might not have enough torque and being overloaded. In that case you might want to upgrade to a servo to something with a higher torque rating and/ with a metal body for better heat dissipation

I would also check all your steering linkages just to make sure everything is moving freely and not causing the overheating issue