Welcome to the club...
I purchased this router for the dual-band performance as well. Obviously, it's severely lacking. I want my money back, but that may require a small claims court appearance as I'm well past my 30-day return. Plus, tech support keeps their mouths shut when it comes to any performance issues with this router. I finally decided to take a risk with D-Link after avoiding them for years for more favorable Linksys products, but Cisco started to severely limit their routers after the "WRT" line (their new routers with irreplaceable antennas, clunky firmware, and limits to prevent using DD-WRT and other such derivitives) so I decided to switch to D-Link for the first time.
Sadly, it may be the one and only time I ever use D-Link again. The lack of communication and the hyped, over-priced hardware from D-Link only exacerbates the situation. How in the world they ever expected this router to be considered an "HD" streaming router is laughable. This thing can't even go through a standard 2x4 wood-and-drywall wall much less stream HD movies/TV across a house.