Hi Kira,
Just to confirm. Yours is RT-N66U? Or RT-AC66U? Which Merlin firmware are you on?
VQ engineer came to my place to troubleshoot. Using AC66U he can hit the DL speed at 600Mbps but once plug back the new N66U (Avertek replaced my 2.8 years N66U), the DL speed went down to 220~240Mbps. This is tested with the VQ engineer's laptop and also my pc desktop. I wonder why it happens. Totally weird.
The firmware I am running on the N66U is the latest one which Maylyn has put up. ASUS TW also told me to get the N66U replaced. But still the same issue. I wonder if any other bros facing the same issue. Can't be so suay I get 2 lemons. 2.8years apart.

