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.
<DIV><FONT face=Arial size=2>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