I agree with bbc. If you dont have the 27.5's laying around try turning your air screws in to about a half turn out and take a ride and see if it performs any better. If its "ratty" or sounds like its breaking up it's usually a lean condition. I still think your mains are pretty large for having fatties. They are more of a bottom end pipe and don't require a big main jet. For comparison, I am running T5's, ported motor, ported cages, advanced timing, shaved head, and I am running 320's at 1400 ft elevation. Just a thought.
-Ryan