Was driving to lunch. Looked at gauge after 10 minutes and firmly in the red. Cut off AC, put in neutral, and coasted at 45 mph down a hill. Returned to normal. Back on drive, accelerated uphill and temp spiked again. Back in neutral for a bit of a coast and back to normal. Made it to lunch with no issues. On way home, started to spike again at 45 mph. Then returned to normal. Engaged AC for rest of drive and no issues. Got home and popped hood. Reservoir low but not empty. Filled it. Ran on idle for 15 minutes when, no issues. Drove it back and forth to late nine holes with the wife - 10 minutes each way with AC on, 3 minute wait at stop light, temp gauge at normal both ways. Thoughts???