Originally Posted by pizzaguy

Overfilling also can cause a saturation of the charcoal canister - which often corrects itself but sometimes, it means an expensive repair!

If the gauge is THAT far off, the most likely cause is a bad sending unit in the tank. I can't say anyone has ever had this happen, but as our cars age, we will see failures we've not seen before.
The issue CAN be in the instrument cluster, but most likely, the sending unit has a problem. Personally, I am doubtful it is a connection or wiring problem.