Dennis,
Based on what I have read and by experience, a symptom of overheating is reduced power. Your ESC likely has a high temperature protection feature that will reduce power to the motor. This will (theoretically) protect the electronic components from being damaged by excessive heat. If the temp gets too high, expect to see a motor slow-down until the timer times out. Once on the ground, take off the hatch to provide as much cooling as possible. If you have asbestos fingers, CAREFULLY touch the ESC, motor and timer. They likely will be too hot to the touch and will remain so for what seems like an eternity --- probably no more that 5 - 10 minutes, but we modelers are an impatient, restless sort. If you are lucky, the thermal protection features did their job and the airplane will live to fly another day (after appropriate cooling modifications!)
Kermit