Try v1.0.1.8g that came out on August 2nd. I also had the same problem and was ready to give up but this firmware plus the latest Asus firmware that resolved the 5Ghz on the RT-N66U made my life easier. So far, so good!
http://support.asus.com/Download.aspx?SLanguage=en&m=EA-N66&p=11&s=1
ASUS...