Replaced gas cap, evap solenoid and still P0446 cel code

[1sicg8]

As stated in the title these parts have been replaced and still everytime I clear it with a scan tool it will eventually throw a P0446 cel alone. Nothing else just that code alone. Everytime it will stay off for about a week then comes back on. It's bugging the hell out of me. Not sure if it is vent valve because I did a little research and people state it throws other codes along with the p0446 cel with bad vent valve. Anybody have any suggestions/advice?

[-Ray-]

Have someone with a Tech II cycle the evap just to make sure it's not the issue.