Any air entering the engine unmetered can cause this, vacuum leaks especiall,y also the oil contamination issue with the K and N, but you probably eliminated that, is the K and N off, the sensor cleaned and the condition is still there? Lots of problems with parts stores rebuilt MAF's also. Check this link also.
http://service.gm.com/gmspo/mode6/pd...t43WXLD_yE.pdf