sounds like the dreaded sending units. they can and do go bad ( see my post on gas woes.) bought a new tank and it had a bad sending unit in it so, once replaced it works fine. You may want to just go ahead and contact c+o and get a new 50 gallon tank to replace the 2. I also have my 2 if you want to try them but it is a pain in the butt to replace them since they are the old style. Steve