Screwy Gas Gauge

[Accelo]

This is a known issue with the fuel level sensor. It is part of the fuel pump. I suggest replacing it. Not a bad job. Remove the tailgate, unplug the wiring and remove the screws from the fuel fill. Loosen all the bolts, box hold-down bolts, on the passenger side and remove them from the filler side. Lift one side of the box and insert a 2x4 to hold up. Takes two people for this part. Then you have access to the top of the tank. I have completed this on several trucks, and all of them had the same issue. This approach is often preferred over dropping the entire fuel tank, as it can save time and effort.
Cheers.