I deal with this sort of thing all the time at work. It sounds like you either have a bad cluster ground or the most likely is the cluster is failing. GM clusters are crap at best. The cluster on that year Cavalier is tied into the anti theft system I'm pretty sure. So a junk yard cluster wont be a plug and play. But if you find a shop that has a Tech 2 they can program it. Check your powers and grounds @ the cluster first.
80 Malibu. 496 pump gas.
6.33@109 n/a 1.38 60ft. With South Side bars!
9.84@135 100 shot.
A stupid question is better than a stupid mistake!