Strange fuel gauge problem

[ScottH]

I have a 84 GMC 2WD stepside that came from the factory with dual tanks. When I got the truck the PO had removed the RH side tank but could not remember why. So after checking it out I have come to find that the fuel gauge is off by about a 1/4 of a tank too much. I tested it with 3 different sending units, all at different levels, all with the same results. Also changed out the fuel gauge with another used one I had, same result. Not sure if the LH tank is the same as I dont have it on the road yet.

Does anyone know what might cause the fuel gauge to read more than it should? Anyone have a similar situation?

Any info or suggestions are appreciated.

Thanks
Scott