Ford Double Gas Tanks

I have a 1980 Ford 150 with double gas tanks. The tanks won't take gas right. I have to baby the gas pump to put gas in. The front tank really gives me problems. I have cut the flaps out of the tank neck and that didn't fix it. The little lines on the neck itself are not plugged.
What is wrong?

is the filler tube being squeezed any where between the filler door and the tank?

No, I can't find anybody who knows. The truck has been changed to a fuel injector system instead of the carb. Would that make a difference and if so what can be done to fix it?

if im correct you should be able to drop a tank and check the neck relativly easy. In about an hour or so with simple tools. Id do that and find out in an afternoon instead of guessing...;) tell us what you find!