I was having the same problems, for about 6 months... And I think I fixed it in the oddest way...
I made my screen a tab bit smaller and lowerd the brightness. (Not the Screen resolutions on the video card but the buttons on the moniter)
And after that all my lag just up and gone. I tested it by putting to the old settings and had the same trouble even in window mode, changed it back and everything is working again, even changing channals faster...
I've got two threads that say the same thing as you. Do what I said and also do this http://www.youtube.com/watch?v=9_hVwD91D7w
Helped me to the point I'm not lagging nearly as much as anyone else o.0
I made my screen a tab bit smaller and lowerd the brightness. (Not the Screen resolutions on the video card but the buttons on the moniter)
And after that all my lag just up and gone. I tested it by putting to the old settings and had the same trouble even in window mode, changed it back and everything is working again, even changing channals faster...
I've got two threads that say the same thing as you. Do what I said and also do this http://www.youtube.com/watch?v=9_hVwD91D7w
Helped me to the point I'm not lagging nearly as much as anyone else o.0