If I remember right, the vent tube and filler tube, enters the tank on the end, pretty close to each other.
If this is a problem you've had from the start, I would guess the vent tube is either plugged, or, the nipple it hooks onto at the tank is plugged.
If that is the case you will have to drop the cover to access the end of the tank. If you are lucky, you might be able to get at the clamp and remove the vent hose to check it out. If the hose is clear, then the only other option would be the nipple going into the tank is blocked.
Good luck, and let us know what you find.
2008 Cruiser CF26RK
2013 Ford Eco-Boost
Heavy duty payload - Max tow