Some gasoline will form gum and varnish as it sits for a long time. The best bet is to drain the tank and then remove the fuel pump. From there you can feel the bottom of the tank to inspect for sticky residue, gum, dirt and rust. Use MEK or acetone to clean up any residue you find. Be careful of the fumes and keep them away from painted surfaces. They are powerful solvents and breathing too much of the fumes isn't good for you.
You will also have an opportunity to check the fuel quantity sender float to make sure it isn't stuck and that it moves freely. Use a little bit of high quality blue silicone on the fuel pump cover seal when you reassemble the tank.
You will also have an opportunity to check the fuel quantity sender float to make sure it isn't stuck and that it moves freely. Use a little bit of high quality blue silicone on the fuel pump cover seal when you reassemble the tank.