Most likely, it is the pathway between you and youtube.
Open a CMD window and type tracert youtube.com
It will give the response times to each portal and any that times out will slow down the connection. However, you cannot do anything about the portals, unless someone there notices.
Series 2 (80 hrs,PLS, Retired)
TiVo HD 1TB (157 HD Hrs, PLS, "S3HD")
Roamio, Oh Roamio!
The TiVo Apocalypse begins on Sat 2013 Feb 16 00:00 GMT!