rwdfan

This hasnt been mentioned yet. He flushed the radiator. How about you go back and make sure all of your clamps are tightened or the system has air in it? System gets up to pressure, starts leaking coolant and taking on air, air bubbles pass by temperature sensor, temp spikes. Gets on highway, rpms drop, problem dissapears. Try checking your clamps, then make sure your fan is coming on, then burp your coolant system for any air, check your coolant to water ratio, and then come back and tell us what you found out! Good luck.