Fuel sending unit.. or?

[bleucrew6.2]

I just realized this morning at the gas station that my left fuel tank was full, even though the gauge read less than a quarter tank. I don't drive the truck on a regular basis, or keep track of fuel levels until the tanks get low, so its hard to guess when this occured.
Three years ago I replaced the rusted tanks with plastic ones. Two years ago I replaced the solenoid tank switch. Never had any issues until now. I'm not sure where I should start looking. Any ideas?

John

[Warren96]

If the tank reads full, when it should read 1/4 it sounds like you may have an open or loose wire on the connection between the sending unit and the gauge. How about disconnecting the sending unit plug where the wire comes out of the tank and read the gauge?