gas cap leaks at higher elevation

Hey guys. first things first: 91 cherokee 4.0 aw4, 33's, 6" lift

this has only happened to me a couple of times, once on independence dayatriot:, and once a couple months prior. I'll be out wheelin and getting up to higher elevations and start to smell gas, so I stop and look around and can actually see gas leaking from inside the gas door. it doesn't seem to be running poorly, but when I restart it after letting it sit a while it takes extra long to start. Also while I'm letting it sit, I loosen the gas cap a little, not a lot ( I just took it off the first time and it spewed gas all over me:flame, just enuf for it to vent the pressure out of the tank. the first time I was heading over a pass, the peak of which was about 9k (leaving from 5300), and it happened when I reached the summit, the second time, it happened twice heading up over 10,200.

Anyone dealt with this before? do I need a new gas cap? :repair:

Make sure the charcoal canister is good and is getting vacuum. There should never be pressure in the tank.

how do I check teh canister? do I take it out and try to blow thru it?