Yeah, streaming video is an issue with this firmware, I can measure 15mb download on a speed test and streams from multipal sites can't stream cleanly. This has been happening for some time however, and Im in a position where I don't know if its the router or the ISP. However after looking at some speed tests it does appear to be the router, I don't know what is causing this, it could be like you say; a DNS issue, which has been an issue for d-link for years now.
On a side note, because of this streaming issue, uploading also seems very poor and completely unstable, good one min, next the whole upload drops. There's no stability what so ever on the upload.
We get back to the router being able to handle a consistent stream of data, and it still can't do that yet, again, I have no idea if this is all related to the DNS issues on the router, or just router configuration. It does it factory default anyway, and I haven't found one setting that truely improves streaming, even turning everything off, and I mean everything, from gamerfuel to WISH, to firewalls and SPI's and wireless, nothing seems to help the streams.