Dear RS;
Make sure the cap is a 'vented' one. The line you speak of is an 'overflow' tube & won't vent if the cap is wrong.
With the cap off, pull the line(imput)to the pump. With the vehicle sitting level it should have a full flow squirting at least 1" or more.
If not; You have a restriction in the tank or the line. Repete the proceture (if restriced)by removing the line from the tank & checking. If still restricted It's in the tank or pickup tube somehow.
I can't recal if the 'pickup'tube is part of the fuel guage (sender)or not. If so, some models have a filter that is part of it and sometimes clogs. Also the pickup tube itself (inside tank)can clog.
Remember; Tanks are usually above the pump so the fuel can "gravity feed" with It's weight (8# per Gal.)pushing it.
It's just a "process of elimination". You'll find it.
Good luck, John M....
