Hi. Here is the diagram for the fuel gauge circuit. You will see that the ground wire for the sending unit is black/white. Make sure this wire is grounded at the pump connector. If ok, you can ground the dark blue/orange wire at the sending unit connector and the gauge should go to full. (If its already at full and stuck there the wire may be shorted to ground somewhere) The wiring runs along the frame on the left side to the front of the truck. Behind teh splash shield at the left front wheel well you will see a junction connector. The wire runs through here before it goes to the instrument cluster. This is a good area to find damage or corrosion.