i have an 05 1500 4x4 with 79,000 miles. It has ran fine then the other day on the hwy it overheated, so i stopped and let it cool down. it didnt leak any coolant so i figured the thermostat was stuck closed. well i put a new tstat in today and still does the same thing, from a cold start it takes about 5 min until the temp gauge is passed the red. It doesnt appear to have water in the oil but im still worried about the headgasket. could it be the waterpump? any help is appreciated.