I have the same problem with my 86 dolphin, but the gauge is in the dash, and yes I have narrowed it down to the sending unit. The sending unit is whatever the chassis is, for example my chassis is an 86 Toyota pickup with a 22 rec motor. Now granted this is not an easy task to drop the tank and replace the unit, so while it is down you should clean or replace the screen on the fuel pump. A good source for the unit is jcWhitney.com, or a junk yard. I have not installed my unit yet, cause of snow and no garage, but I am very anxious to get it installed, have a big trip planned for March.