Check for boost/vacuum leaks also. Could be as simple as a charge pipe coupler torn or popped off. If you have an accurate boost gauge make sure you are seeing the expected boost. A small leak under even a light load will richen it up but not stay under load long enough to pull the trims far enough to set a light.
Vacuum leaks are a bitch to troubleshoot on boosted cars because it runs rich under boost and lean in vacuum and the computer goes back and forth on the corrections so it looks like its working properly.