Fuel gauge not working 2005 silverado 5.3 vortec

[Krayten88]

So today went and put some gas in the truck then went about my business and it was about a hour and a half later I turned the truck off and when I came back I noticed with ignition off it was setting at a quarter of a tank and when I turned it on needle went past full and im guessing it only has about 3/4 to 1/2 a tank full and it doesn't move till I turn it off then it sits at 1/2 anyone know what it can be gauge or maybe something on the tank????

[T.J. Sponable]

The fuel sending unit is on the pump. If your dash is doing a full sweep at key on, then most likely its a bad sender or a wiring issue. If it is the sender, do the whole pump.