I had an issue where the EA4500 was not transmitting Wireless N rates. I did some searching and found that when you disable WMM the router will only transmit at Wireless B/G rates on 2.4 GHz.
Just re-enable WMM and you will get your Wireless-N speeds back.
To re-enable Wireless-N rates:
Login to your Administration page (typically at 192.168.0.1)
Click “Media Prioritization”
Finally, enable “WMM Support”