Occasionally while shooting in auto/portrait my shutter will stay open for 1 second or longer, for no ...

Have you tried to reset the camera and reboot the firmware? I had that problem with a friend's camera and it simply worked.
Other thing is: are you using the original battery or a third party battery? sometimes bad quality batteries are creating such a problems like shutting down the camera, shutter lags...

I hope it helps, if not let me know