2003 Chevy Silverado

That's an easy one. But you won't like the answer. The fuel pump/sending unit's variable resistance potentionometer (thingy that tells your gas guage how much fuel you have) is bad. It is a COMMON problem with 1999-2004 chevy's. My unit would slam down to "E" if it was below 1/4 or above 3/4 of a tank. The only way to fix it is to replace the sending unit (around $200.00). I did it to my truck and I am so giddy to know how much fuel I have instead of estimating mileage by the Tripmeter.