I have the 3.9L V8 and when I first drive the car,as the engine warms up it goes to hot and reduces the engine power.But if I turn the cabin heat on hot and turn cabin fan on high the temp will stay normal,and after a few minutes I can turn it back down and everything is fine.Then if I drive the car within a few hours it doesnt do that.I also just had thermostat replaced,what could it be???