Fuel Gauge Problem

Beats me how so many never consider the gauge to be the fault. Fact is there is much more mechanical than electrical inside it. Now consider its age and its lifes labor compared to a temp gauge or any other. Can you imagine wear in the instruments movement eventually causing a seesaw effect ? That is what you're looking at. A secondary programmer inline might make that needle stand at one or more positions between full and empty for some length of time. Good luck with it.