i have a 97 tahoe, 5.7 vortec. 4x4. when i fill up the tank with gas, i get pressurized fuel coming through the evap canister. it fills the canister up and overflows. i did some research and could only find something about the pressure relief valve between the tank and the canister being stuck open? anyone got any ideas? once the tank is down a few gallons it doesn't do it anymore.