Check the advanced Wi-Fi adapter settings in PROSet.
http://www.intel.com/support/wireless/wlan/sb/CS-025393.htm?wapkw=wifi+settings
Look for "HT Mode/VHT Mode"
This settings lets you select HT Mode (High Throughput mode), VHT Mode (Very High Throughput Mode) or lets you disable both modes.
HT Mode supports 802.11n compatibility
VHT Mode supports 802.11ac compatibility.
Check to see if you have this setting in VHT Mode