I AM 2ks4

For the past 2-3 months when I would accelerate under WOT my car would be limited to about 10psi. If I let off the throttle and and went back to WOT it would be fine and hold steady at about 17-18psi. This would happen maybe 1 time every 2-3 weeks. The first time this happened was at the drag strip and I heard a "pop" and the boost went to 10psi. Since then I haven't heard any noises what so ever. Last week I had some RS4 IC's installed and the car was working great. I just came back from a 1300 mile trip and along the way I noticed that the car felt like it was down on some power. As the trip progressed I felt more and more surging from my car. I was able to pinpoint it so it would happen in 6th gear with about 20-30% throttle. The needle on my boost gauge would jump from 2-5psi constantly going back and forth. It only would happen with the 20-30% gas. To prove that my car was down on power, I came across a guy in a newer SLK320 who was wanting to run. From 80-120 downshifting into 4th gear I was barely able to walk him. It could be the extra passengers and 300lbs of crap in the trunk, but I doubt it. I did a pressure test and did not find any leaks and all of the hoses to/from the IC's are tight. Any ideas on what it might be. I am APR stage 3. Thanks

Fraser@PNS now w/S6

BPV's?