Fuel Gauge problem

I have a 2000 Pontiac Grand Prix. The fuel gauge almost always stays on full. I fill the tank up every 288 miles to make sure I don't run out of gas. On occasion when I get about 50 to 80 miles away from when I normally fill up, the gauge will suddenly move down to empty. It will stay there for a few miles and then move back up to full. I would like to fix it myself if I can. I just need to know what the problem most likely is and how I can check to see if that's the problem.


Thanks for any help y'all can provide.