Did you try replacing the gas cap? Mine just started leaking a few months back and threw the DIC message. The original looked okay, but it wouldn't seal. That'* only a 10 dollar solution if it works. I suggest that if you are still getting the Check gas cap on the DIC, to start there.

I find myself replacing the emissions vacuum fittings about once a year. The tee on the fuel regulator, and the reducer where the other end attaches to the */C vent valve also cracks,

I am getting the bouncy RPM at highway speeds light throttle load. SES light on (can't remember code) and constant message to ck the cap. Replaced the cap, reset light, and it was back within 150 miles.

Believe it could be a leak in the system somewhere, but no idea where to look.

Replaced the motor and every line that looked even remptely suspect.

other then the RPM studder ...car runs great and delivers great mileage.