2001 Saturn with automatic shift problem

I was in heavy traffic in L.A. for a couple of hours last night - start and stop at 2 miles an hour – and when I finally got into light traffic on a level stretch near home the automatic shift wouldn’t drop out of first into 2nd or 3rd or whatever. It just revved up to about 5000 or 6000 RPM until I tapped the accelerator and it finally responded with a higher gear.

This morning I took it to a shop, and it seemed ok and the repair guy drove it for a half hour and couldn’t get it to repeat last night’s performance. He checked the transmission fluid, and it was ok. I drove it home and it behaved well.

What’s this about? Heavy traffic a strain on the transmission? My imagination? Is this likely to happen again? Am I nuts? Do I have part time gremlins?

I may well be wrong, but this sounds like a dirty shift solenoid or a faulty VSS (Vehicle Speed Sensor).

When was the last tranny fluid and filter change?