I think ISP problem.
With my 50Mbps Surewest connection, streaming from YouTube max's out my line when doing 720/1080p, but on U-Verse, I can't even do 480p at the same time. Could be routing to, but its been this way for years.
My Internetz: Surewest 50/5, CenturyLink 10/896, AT&T U-verse 18/1.5
Computer: i7 email@example.comGHz, GA-P67a-UD7-B3, 16GB DDR3, GTX 580 and GTX 260, Corsair 750W, Antec 1200
same problem even on comcast, sometimes.
my youtube speedgraph sometimes shows 50 megabits, then others 5 megabits
it's all over
i have comcast xtreme 105, it's not me. my connection is perfect, just yt.