this is on a 99 Z28...noticed that while i was driving the speedometer, tach, and odometer shut down. All other gauges worked fine. Then next time it was driven it all worked again. I was thinking it could be a loose connection in the cluster or the fuse box, i was just wonder if there was something like a VSS or another sensor that could be going bad that would cause all three of these gauges to drop out but nothing else

 

I had this happen to me on another Pontiac when my alternator was on the way out. There was enough juice to keep the car running as well as most of the gauges, but not enough to drive the odo and tach.

You may check the voltmeter gauge and make sure it isn't fluctuating or reading below 12V? If so, you may have a general issue with the electrical system.