Welcome,That is by far the most common reason for this to happen. You will need to pull the fuel pump module out and connect the connector back on then slowly move the float and watch the gauge. If it moves from empty to full when moving the float you know the gauge is good. We replace far more sending units than gauges for this type issue.LJ
Whats it like removing that. Haven't looked yet. Have to drop the tank?
it is full
Can I not do it with a full tank? I have the support to lower it full? What issues will that cause if the tank is full?