The command on the switch port is something like power inline static max 20. Make sure you have the right code on the switch that allows it. Don't know it off the top of my head, but I think th eminimum is 12.2(44)SE.
For 802.11N, you need to make sure that WMM is enabled, that you have bonded channels to give you 40mhz channel width and that you either have an open ssid or using WPA2-AES. WPA-TKIP is not supported for 802.11N.
When bonding channels in the 2.4GHz, you will have overlapping channels if you have more than one ap and is suggested that you only bond channels in the 5ghz.
Looks like your already running MIMO since you have 72mbps already.