Id remove the sending unit and inspect. Outside of the tank, hook up the hot and have a ground ready. Turn the key on touch the ground wire to the top and see if the float arm will change the reading and if its accurate or not.
~ BD. "You won't find me in an old folks home" Pioneer Florida Cracker 1958 Apache Stepside 1958 Apache 1/2 ton Panel 1959 Apache 1/2 ton Panel