Fuel gauge going crazy!

Sounds more like a bad sending unit in the tank. Or the guage on the dash is bad.

I have had this same issue on a bonneville, what sometimes happens is the fuel senser, the sensor that measures how much fuel in the tank you have, sometimes it gets corroded. Go to any auto parts store and pick up a bottle of Cheveron Techron, it should be in a black container thats round towards the bottom and a long neck, it costs about 8 bucks and pour it in on a almost empty tank, this should clean up the sensor and even the fuel lines, combustion chamber ect. I have done this many times for customers that dont wish to replace the sending unit as most newer cars, the sending unit, fuel pump and tank are all in one, so if one goes back you need to replace it all, can be costly, so try that chevron techron, how this helps. Let me know!

Yep, good call, LSUSSEL must work for Chevron lol. Here is how to change it out so they can fix the problem. Luckily there is a trap door, so you don't need to drop the fuel tank. Check out the images (below). Let us know if you need anything else.