Thank everyone for their response. Here's a new clue to the puzzle. The outside temperatures have now settled down to the high 70's - low 80's. I am now having no overheating problems at all, same as before the 90 degree weather. This is apparently a high outside temperature problem. If that helps let me know. I can't see where it could be the water pump only acting up in temps in the 90's nor the radiator. I am thinking a clutch fan problem. I welcome all ideas.

 

You'll like this one. We had a truck that would never overheat except at about 55mph. Had everything checked and they said everything was fine. Took it to another shop and they said someone had put the fan on backwards and at the speed it was overheating the airflow was likely balanced between what the fan was pushing forward and the incoming air was pushing back so there was no air movement. He put the fan on correctly and never again a problem.

 

atta3 - When something in your cooling systems is not working right, hotter outside temperatures are when you will notice it first. The ability of the air to absorb the heat from your engine is much worse as the air temperature rises. Outside air temp can make a BIG difference in your engine temp if the radiator or water pump is not working right.

On the backwards fan story - I've also seen thermostats put in backwards. Engine melt-down resulted on a hot day, after the vehicle had been run for a week in cooler weather.

Can your radiator get corroded in 4-5 years? It shouldn't, but it can. The 2 cars I had to have the radiators rodded out on were 5-6 years old. Overheating problems were immediately solved.