Tank leakage

[Mastiff]

I installed a new plastic tank in my K5 about 8 months ago. All was well until now suddenly, when I fill up, right as it gets totally full, it burps a bunch of gas out onto the side of the truck. This last time, after doing that, it started dumping gas out from somewhere at the top of the tank. I looked at what I could see and it all looks normal. I tapped the lock ring and it seems tight. The only thing I could see is that I might have the breather hose to the filler pinched a little. Could that explain the burping at least?

I'm assuming I'll have to drop the tank again, which I hate. But if anyone has any ideas, that would be great.

 

[bp71k5]

Mine does the burping thing when filling up at stations that don't have vapor recovery systems. OR and WA were two big ones I remember.

The big vent hose needs to be very clear and not have any low spots in it otherwise gas sits in the low spot and won't let air through.