Another thought....might be an old sending unit float left in the tank by PO getting sucked into the tank outlet when it's low on fuel. Just GUESSING???
Tim
"Pay attention to the details! It ALWAYS pays off."
1949 Chevrolet 3100 Series 1/2 ton Pickup 1964 Chevrolet C10 (Ol' Yella) (SOLD) 1958 Chevrolet Biscayne 2 door (SOLD) 1970 VW Beetle