mustangcobra93

I have a '08 Sierra with the 5.3. The motor has 231,000 miles on it. The check engine light has been on for awhile with no drivability issues. Yesterday it started blinking and the truck starting running rough. After a few minutes it stopped blinking and the truck ran ok again. It stumbles at idle now. I pulled the codes and here is what came up: P0606, P0300, P0521 & P069E. Any idea what might cause this concoction of codes?