My '95 F-150 overheats at highway speeds even though I have replaced the thermostat and water pump. The pump was leaking, being the reason for replacement, and I changed the thermostat just because of the high mileage on the truck. But now, at sustained speeds at 55+, the temp. gauge pegs for 10-20 seconds then falls back to normal temp, hangs there for a couple of minutes and then starts climbing back to the high temp side of the gauge. Just driving in town in stop-and-go traffic the temp. stays in the normal range. Could the lower hose be collapsing? I've kept an eye on coolant level and that's at normal level. I would appreciate any insight to this problem that anyone might have. Is there a way to replicate driving conditions in the driveway? Maybe place the truck on jackstands and block the airflow through the radiator.