Need help with gas gage!

I have a 04 GP 3.8L. The gas hand is reading empty and the warning light for low fuel is coming on even after i just put $20 in the tank. Then it reads full when i start it up but its not full or on empty. It just reads wrong at random. I was wondering is this something i can fix or do i have to take it to a shop?

The fuel level sensor can be replaced separately from the fuel pump module (AC-Delco part # SK1051) but it requires removing the fuel pump module from the tank. There is an access door under the carpet in the trunk for the fuel pump assembly so the fuel tank does not need to be dropped to change it. It's not a technically or physically difficult job, but the area is a little cramped and you want to have a well ventilated workspace so gas fumes don't build up.

Rich, I was always curious if the newer GP's, 04+ had the same access cover in the trunk that the 97-03's did. Guess that answeres my question.