Overheating 1966 rebuilt 302 at highway speed 50 and above approximately 230 degrees. Temperature normal at speeds below 35 mph. Replaced radiator,heads, head gastets installed correctly, drilled out steam holes in block, thermostat, hoses, installed electric fan, high flow water pump, bypass hose, checked timing and set carburetor. At idle engine heats to 195 and electric fan comes on and temperature goes back to 180. I can run car at highway speeds and car temp will go up to 230 I can slow down and temperature will start to drop, can park and idle car and temp goes back to 180. Have tried water wetter,straight water, and 50/50 antifreeze. Can a high flow water pump push water through radiator at high speed to fast to cool? Any assistance will be appreciated.