Dalej, I try to always keep the tank full to minimize condensation, and it is always full when I leave for a trip. Since I have never noticed any movement of the gauge at all, I assume I have a bad gauge, bad sensor or broken wire. Odds are, it is the sending unit.

I would try to ground the gauge to verify if it moves at all, but I think it has 3 different wires on it. Maybe I can use my multimeter to see if I can determine what is hapening with the gauge. I suppose about the worst thing I could do is blow a fuse or burn out the gauge. Or maybe catch the bus on fire!