cause of pressurized fuel tank?

[TDS-MN]

Hey All,

Ok, so if it's not one thing, it's several at once it seems with this truck.

But, the one that I'm chasing right now is, what could be the cause ( and remedy) if the fuel tank seems to 'pressurize' while driving? If I keep the gas cap loose, I don't have the problem. If I get it maybe half-a-turn too tight, fuel ends up pushing past the sending unit on top of the tank, and running down all over the place. Could this just be a vent hose somewhere that isn't allowing pressure to release? But curious how I'm getting any pressure in there anyway, it's got teh mechanical fuel pump on the engine, and I thought that the whole thing was gravity fed from tank to pump anyway.

Tank was replaced by a local shop a few years ago. This issue actually didn't even show up right after that, but was actually a few months afterward that I first noticed it. I have typically been just leaving the gas cap ( my second one, after replacing it thinking maybe it had clogged venting itself or something) loose, but mostly screwed on. Stock 305 w/ quadrajet, by the way.

Took the truck in to the exhaust shop this morning to fix an undehood exhaust leak, probably either donut gasket or manifld gasket is my guess. The noise that is making really makes driving the truck somewhat unpleasant currently. Hopefully I will at least be able to get THAT solved today. . . .