Also, have you set the endpoints for the throttle on your radio? With the radio and car on (not the engine), hold the throttle wheel fully to one direction and reduce the EPA until you see the throttle linkage start to move and leave it there. Do the same for the brake. This will make sure that the servo isn’t straining at full lock.

Also, with the servo disconnected make sure that the throttle/brake links on your car move easily and freely too, otherwise this could overheat your servo.