Apple TV 3rd gen, latest firmware connected over ethernet to Airport Express (current gen):

I noticed a few months back that AirPlaying video from Vimeo, YouTube etc would be really laggy and drop back to a very low resolution stream. YouTube for instance will only stream at about 140p res! Im not sure what's happened, because I was able to stream 1080p stuff perfectly fine months ago. Software updates are uber slow now too. 

DNS is acquired from the Airport Express (203.97.78.43), but I have tried manually adding the DNS addresses too.

Using the direct link feature from the YouTube app to my LG TV works fine – it loads in HD perfectly and fast. But I really want AirPlay working fine. Local AirPlay streams fine as well, it's only when I have to stream something from the www that it fails.

Any ideas?