that would be my guess. Maybe rent a movie from itunes and see if you have the same streaming issues. Could have also been the source of the streamed material.
I'm on cable internet. I have the level above basic to allow for more bandwidth usage per month for $10 extra/mth. Even at the basic though, I was getting 20+mb/s.
Your dl speed seems very very low. Check that, I just checked the AT&T site and that seems to be what you should be expected...