Nissan Maxima: Overheating 1999 Max

Had this car since new and never had a problem until a few days ago (66K on
the clock). Wife sat in a traffic jam for 1.5 hours with the AC on and the
needle started to climb. She caught it before it topped out and pulled
over. Had it towed home and I replaced the thermostat -- even though there
was no indication that it was bad.

The water pump is good - no leaks or bearing whine, and the coolant/radiator
appear to be good. (been flushed and filled several times since new). The
fans work fine, shift from low to high as the car warms up, and it will not
overheat in normal driving. The sensor passes resistance tests as set forth
in the manual. Hoses are new and coolant circulates as one would expect.
Can't find a "hard" cause/problem.

My wife is now afraid of it and won't drive it until it is "fixed." Anyone
have any thoughts or experienced similiar problems?

CW wrote: 
Good suggestion. I should have suggested this 1st myself.

CD