For the last few months I've been having problems with my car losing power.I'll step on the gas and car won't boost above 30 kpa. I brought it in to dealership about a month ago as it was happening every other drive cycle.They took a look at it but couldn't find any codes. They checked the map and maf (stage1)connectors, the wastegate and did a boost test. Everything was fine. They took it for a couple of test drives and couldn't recreate the problem. After picking it up the car ran fine for a couple of weeks but is now starting to act up again. The car has also stumbled from a dead stop a couple of times. Other thing I've noticed is rough idle and hanging revs once or twice. Anyone else experience this or have any Ideas? The only mods to my car is GM Stage 1 and K&N drop-in filter.

 

Fuel trims are about 7% off with the K&N drop in.. Put the stock filter in or get a real tune. Might also be a leak around the o-ring on the lower cp sensor if they didn't mount it right. I know you said no boost leak.