Float arm might need to be bent to calibrate the float level. You can bench test the sending unit out of the tank with an ohmmeter to make sure that it is working properly then adjust the float level. Or you can do it the shade tree way...if your gauge showed low before you filled it and then went to half after filling it, you float probably just needs to be adjusted. I adjust with a completely full tank and disconnect my battery between adjustments. Bend the arm down in small increments until the needle points to where you want it with a full tank. Then you should be good to go. As an added measure of insurance, carefully watch your mileage between your next couple of fill-ups until you are sure that your gauge is working properly. You don't want to trust your newly calibrated float/gauge and assume that when the gauge shows that you still have gas that you really do! Better to use a belt and suspenders approach to watching your fuel by checking the gauge while also watching the mileage so that you don't run out and get stranded. Hmmm....wonder how I learned that!

Matt