Got to be a venting problem...did you try putting compressed air into the tank with the fuel removed? Should not been able to do this if the vents are working.

Hope you find the problem after dropping the tank. Be sure to let us know.

 

I gave my truck to a mech friend ....found crimped hose and replaced, he pulled tank, installed new pump and removed spring on ball .....now I have a good reading of fuel. but............ still cant pump gas at full throttle, have to ease up on gas pump for gas to go in....not sure why he left ball in but I think that's the issue now.
anyways, truck running good except gas mileage but whats new....plugs and wires next.
thanks to all for your input

 

There is no spring on the ball, it should roll back and forth freely in the plastic retainer inside the filler neck.