It was mentioned earlier, but I just want to reiterate two points.
1) That power is exactly what you should expect with that turbo on that dyno
2) Your stumble is being caused by the factory FPR. Either get an aftermarket FPR or swap in one from the older models. I am not guessing here, and neither are the two people who posted earlier about this problem. This is WELL known and WELL documented, get a new FPR or you'll be needing new pistons soon.