Fuel level sender

The other thing you can do is buy a "MeterMatch." There are other copycat gauge correctors on ebay, I think one is called a Dolphin. This is a small box you install under the dash, the sender drives the box, and the box drives the gauge. It has some programmable adjustments to correct the gauge through points on it's range.

You of course will have to "play" a little bit, IE put in enough fuel to be the "safe still running empty" point, etc etc