I believe there was a Ford bulletin on this gas tank filling problem. It seems to me I had the same problem with my first contour.

2000 Black SVT #2639/2760; w/18 OZ Superleggera's, Pirelli Pzero Nero. MSDS Headers,Quaife LSD, CF DF, Borla,,chipped,DMD,Baer Track rotors. Lowered/HR and Koni's; HPP & OMP 3L Valves w/ P&P Heads (thanks Kinger!)