Excessive fuel tank vacuum 99 6.5L diesel
 

The fuel tank in my K2500 6.5L 99 Suburban builds up a good vacuum during use and has so since I acquired it. I've replaced the cap twice with no impact (one was an AC Delco piece with correct p/n the other a locking Stant supposedly correct for the application). To cope, I release the cap after driving or drive with the cap not fully seated. I'd like to finally correct the issue.

Any ideas where to look first? Were it a 72 I'd know where to start but unsure on a 99 diesel. The truck has 44k miles but the tank was replaced according to the Fire Chief of the station that used it. Is it possible there's a vent line that's not properly connected?

I've done some research and similar issues have been correct with replacement caps but as I've tried two already I'm skeptical this is the issue.

Re: Excessive fuel tank vacuum 99 6.5L diesel
 

Maybe they kinked the vent line when they installed the tank.

Re: Excessive fuel tank vacuum 99 6.5L diesel
 

I’ll root around and check for anything obvious. Im unsure if diesel tanks were unique or used any sort of an evap/vent system.