What wireless modes are you using? Under Setup/Wireless/Manual.
Try single mode G or mixed G and N on 2.4Ghz and single mode A or N on 5Ghz?
Channel Width set for Auto 20/40Mhz or try 20Mhz only.
What security mode are you using? Preferred security is WPA-Personal. WPA2/Auto TPIK and AES. Some WiFi adapters don't support AES, so you might want to try TPIK only.
What wireless devices do you have connected?
Any cordless house phones?
Any other WiFi routers in the area? Use
InSSIDer to find out.
Turn off Short GI and Extra Wireless Protection if you have it. Under Advanced/Advanced Wireless.