Fuel Gauge shows empty with full tank of gas

Lol... Your prime went so long without gas it forgot how to measure how much is in the tank. Probably an easy fix by basically doing the equivalent of rebooting your computer. As in disconnect the 12v battery for a few minutes, which will reset the car back to original settings. You'll lose some minor system presets like radio stations and other stuff but it's easy to get that stuff back.

 

If you've previously had rat issues - there's a high likelihood that they chewed on your fuel sender wires. If the wires has been chewed, it would most likely be attacked at the fuel pump head. There's also the possibility that the sensor arm or sensor itself is damaged. If you have access to Techstream, you can look at the sensor output directly. Have you tried driving the car in HV mode? You'll need to burn-off some of that gasoline, so it doesn't overflow - if you remove the fuel pump assembly to inspect it.
You can inspect that area, using the video below.