The fuel gauge could be the sending unit.
You can check the gauge by grounding it on the back and have someone watch the needle. I needed to replace the sending unit in the tank(http://www.wemausa.com/sensors/level...l#.V1hAAab2aAY).
To verify the sending unit, you can pull up the floor sections (8 screws, 4 in each corner of each panel and pull up hard). Then it is just a matter of ~6-8 bolts holding it in the tank. Take it out and slide the float up the rod. If the gauge moves, then the float was probably fuel logged.
Get a yard stick and put it in the hole and re-order based on the depth of the tank, new unit will be more accurate. Stock I found reading E with ~1/2 tank left. New sending unit I could get within a few drops of fumes.
What truck are you pulling with?
2004 Supra Launch 22 SSV
5.7L Indmar Assault
"One More Hour"