Your symptoms were very similar to mine. It worked fine for nearly a year, but awful after that. After contacting support I got a replacement which seemed ok, but performance was still a bit poor compared to what I would have expected. In the end I p...
Big thanks for the guys at Cisco support. I had the Beta software within an hour of contact, although it didn't fix the issue, we have come to the conclusion that the hardware may be at fault given that it worked flawlessly for 5 months before acting...