truck over heated (water pump went without me knowing it) lost coolant on the highway. When I noticed I pulled off the next ramp, and the temp gauge spiked to red. Truck stalled... I let it cool down.. drove home (1/2 a mile tops) stalled again. Coolant was empty. Did a coolant flush, filled radiator, & now truck just stalls immediately .. idling at less than 500 in neutral. No power.. will drive but everytime. I brake it dies. What do you think? Obviously the overheat did something. Hopefully no melted pistons.. how would I know im thinking head gasket.