When you remove the gas cap, do you feel a vacuum or hear a rush of air? If so, the valve in the cap is stuck shut. This is very common with certain new caps.

This prevents fresh air from entering the tank to replace the fuel being removed by the fuel pump.

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)