Here's his situation:

http://www.ls1gto.com/forums/showthread.php?t=195002

Basically, the tuner has spent a good amount of time finessing the VE tables in SD mode. When he switched the car back to MAF, the car dies around 3,500-3,600. He'll post the logs up tonight which the tuner sent him. I've seen the dyno chart and sure enough things look fine until mid 3k then it's just dead after that (goes dangerously lean).

Bad ECM? Bad MAF? Tune needs more work? Any thoughts? I'm not an expert, just been searching around the forums and trying to give ideas to him.

From what I know, all the tuning was done in SD mode, and all the tuner did afterward was re-enable the MAF with no additional tuning. I might be wrong, but that's how it was explained to me.