The following things you can try..
1. Make sure you are in 5Ghz band, and 40MHz channel.
2. Check wheather any a/b/g client is connected to the same SSID.
3.In IAP monitoring tab, click on your user name and check on which channel & type you are connected.
4. Make sure your uplink is 1000mbps.
5. Last thing, please update your wireless adapter.
http://www.connect802.com/80211n_channels.htm
NOTE: Don't try these in production. [better you check in lab]