Have you tried to re calibrate it with the sender back in the tank and registering where the empty and full fuel levels actually position the float arm?
Maybe the result will be better then a bench calibration where I assume you used both limits of travel on the float arm for programming full and empty?.
My Speedhut fuel gauge is without a doubt the most accurate gas gauge I have ever had (at any point in the full sweep of the needle), in any vehicle. With aftermarket sender.
