Remember realtime services (streaming included) aren't affected even when you're shaped.
Except that if you visit Youtube's "My Speed" page, it shows I get an average of 2Mbit to Youtube, whereas I can download (when there's no shaping) at 420Kb/s from other places.
It's clear to me, if it's not shaping, there's some issue with Youtube accessed from your network or SA in general. Can you look into that? There have been times where, even at 4am I can't stream 140p videos but if I close Youtube, open a download, full speed. So I dont' think it's any issue with my line/setup at home.