Large difference between WiFi speed and direct link speed

Is your WMM enabled?  I had very slow internet speeds for awhile likely a result of firmware update in June but didn't really pay attention to it until recently.  I spent last night troubleshooting it (including downgrading firmwares).  I finally saved my config, reset the router and I was getting full speed.  I loaded my config again and back to 20 Mbps.  I reset the modem and started from scratch fiddling with different settings.  I finally determined it was the WMM.  The moment I enabled it went back to full speed.  With one of the firmware updates it seems that WMM is required to attain full speed over wireless.