1984 300TD Fuel Guage Not Working

I just bought an 84 300TD (Yes, the wagon) and I really like it. One thing that I don't like is that the fuel guage is not working. It jumps all over at times, and at other times it will stay all the way empty (after I just filled it up) or all of the way full. Not sure if this is related, but when I fill it up, I have to put fuel in very very slowly (~.5 gal per minute) otherwise the filler fills with foam and shuts the station pump off.

Has anyone experienced this problem? I am honestly at a loss of where to start to troubleshoot this issue. Perhaps look at the sending unit? Is there a float? Any help would be greatly appreciated.

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