The fuel level sensor/swing arm dealio needs to be replaced.
Dorman makes a replacement part and is pretty simple to replace. Remove the fuel pump from inside the trunk and install the new part and away you go.
The fingers that run across the circut board wear off and or break over time and now it can't read correctly.
Just youtube bonnieville fuel level sensor replacement and watch the video's. Explains what I am talking about pretty well. Though it's on a bonnieville the replacement is nearly the same on a grand prix. Don't pay attention to the prices he paid and where he got the parts as the video is pretty old.
