Gagged At The Gas Pump

Have a 2001 Ford 350 15 Passenger Wagon

The gas will not go into the tank unless I dribble it in, it takes appprox 1/2 hr to fill. Had the gas tanked pulled, air lines & filler tube checked for blockages, there weren’t any. What could the cause be?

Do you top off the tank or do you stop filling after the first click of the gas pump?