It sounds like a failed sender or float. I'd remove it and see. If you want a sender which reads an accurate 0 to 30 ohms and is designed well, there is a seller on eBay (his ID is renbusan) who sells a sender designed and made in Taiwan that is very good and about $29 last I looked.


~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end