I filled up @~6500ft with 91 octane plus octane booster. Drove to ~8000ft and parked. Heard some strange sounds and decided to crack the filler cap and got about 2 minutes of fuel splatter out the filler neck followed by another 2+ minutes of boiling.What elevation are you at, what grade of fuel do you use and once getting the cap how full was the tank starting off and when you tested for pressure?
I approached my issue a bit differently after doing the canister check-valve function check (which did not pass, unless the FSM is exactly opposite of what should happen (not likely)).
At any rate, I still have the OEM canister but on last test run didn't have the over pressure in the tank like before.
I'm not comfortable sharing what I did to my canister until more testing is performed. (I actually did post what I did, but it's burred in a thread on the issue somewhere).
Some say it's the ethanol in the fuel. Others say it's the altitude coupled with the ethanol.
Many say their issue went away after changing the canister. So far my issue has gone away and I didn't change the canister. So who knows.