My 04 LS1 has had several strange occurances with my gas gauge when I filled up. When I started the car the gauge went to empty and my check gauges light went on. The gauge tried to reset itself. Finally it cleared and went to full. It took about 15-20 miles to clear. No effect on performance was felt. This has happened on several occasions. I am running Sunoco w/o Ethenol. Any suggestions or comments.....? I have checked the gas cap and restarted the car. It still took a while to clear the system.