Depending on the router, being an 802.11n router could simply mean it's "n" capable, not that it is set in "n" mode. So the first thing to do is go into your wireless settings and verify the mode. Also, ifyou have other devices that are not "n" that will limit your router.
Also, make sure you are using WPA2 security.
If that doesn't improve it, try checking it with your computer close to the router. (or range extender) Distance and walls can make a big difference.