Gas gauge?
 

I just bought a 2002 chevy Silverado ls extended cab. I filled her up right after bringing her home. I had a quarter of a tank( so the gas gauge said) and she lost power. I figured the gas gauge was broken. So I managed to get it pulled to a gas station. It only took 20 gallons to fill. So I had 6 gallons left. But after I filled it up the truck ran just fine. Any ideas of what this is? Thanks