HD2000/HD3000 losing frames with flash player and silverlight

I have been having issues with both HD2000 and HD3000 on i5 cpus with streaming video using both flash player (hulu.com, youtube.com) and Silverlight player (Netflix.com).

The issue is identical: When streaming video the sound is fine but the video will lose frames and skip forward. This is not a network issue as the skips occur even if the streaming content is buffered well ahead of the current position in the video. The problem occurs even when video is not full screen.

If I disable hardware acceleration in Flash player the problem goes away. There is no client side option on Silverlight to do this. CPU usage and temperatures both remain low when streaming video; the system isn't getting stressed.

I have the latest drivers at this time, 8.15.10.2559. I'm using a Zotac H67-ITX-C-E motherboard on the displayport output to a Dell 30" U3011 monitor. I've had the issue with both I5-2310 and I5-2305S cpus. I have 16GB of memory.

Has anyone had this issue before? Is there any way to disable hardware acceleration completely as a test?

Thanks!

Edit: I have the latest Flash Player and Silverlight. The problem occurs on both Internet Explorer 9 and Firefox 10.

Edit: Deleted replies describing what the problem was NOT. :-|