I have the exact same router and was having the exact same problem. You need to upgrade the firmware version on your router. I tried numerous things but found that was the only thing that worked.
I had version 1.1.00.28 but once I upgraded to version 1.1.00.41, the problem was solved. I now get a great wi-fi connection. If you have problems, call Netgear and they will be able to help you. Hope that helps.