Fuel gauge is reading way past full

Probably your sending unit is bad in truck. Or the wire leading to it is grounding out against frame. Test to see if the wire leading to tank has power with a test light it should be a blinking light or low voltage if it is then it's the sending unit. If you can disconnect the wire and the gauge goes down especially.

The wire going to the sending unit is grounded or the ground is missing from the fuel gauge. Unplug the wire at the gas tank first. If the gauge goes to "empty", there's a problem with the sending unit.

You can trace the wire to see if you have continuity this guide will help

https://www.2carpros.com/articles/how-to-check-wiring

Please run down this guide and report back.