First, youtube is a notoriously poor streaming website. I've done tests at work, home, on various operating systems using various browsers at different times of the day. It's hit/miss regardless of what we do on our end.
Second, for a while now I've started using google dns servers for streaming devices. I discovered this when Hulu would have issues constantly on my playstation 3. Added 8.8.8.8 and 8.8.4.4 as my two dns entries in the playstation's dns settings and RARELY have any issues now. 99% of the time I have flawless playback, where it was 50/50 whether I could even get through a video before. The culprit were crappy time warner (roadrunner) dns servers. Lord knows how they maintain routing tables, but google obviously does better.
I'd suggest using the google dns entries and see if this helps. Might not cure the youtube issues, but might improve things like it did for me with Hulu.