Bob,
Check the connector connections to the fuel sender and the guage. The connectors GM uses (metripak) have a history of loosening up electrially. This will be a tuff problem to locate, you need to check every connector the wires run thru. It even could be a power feed to the IP cluster.
Good luck
Martin "Bob" wrote in message news:hHRTa.135974$Ph3.17519@sccrnsc04... Gas guage on 2000 GMC Sierra 1500 5.3L will go from full to empty in a split second, low fuel light comes on, a little later will shoot back to full. Gas tank is FULL. Any similar problems out there?