Windows 7: Slightly lagging video in all players

I can't seem to get smooth playback with any videos and it's driving me insane.

I've tried WMP, VLC, MPC-HC, and it makes little difference.
It doesn't matter if it's 1080p or low res.
Every video plays as if it has a a very low frame rate; basically a subtle lag/stuttering that gives me a headache if I look at it for too long.
It's not really noticeable until there's quick movement in the video.
I've tried many different output settings in these players, and used several different codec packs.

I'm using a new Samsung Series 7 notebook with a Radeon 6490M card. All the drivers are up to date.
If I can't get this fixed I'm going to have to send this laptop back, something I'd really like to avoid doing.
Any help would be extremely appreciated!

Try installing this DirectX update

I did that and it didn't help.
Video in WMP looks fine until there's movement, and then it has this low frame rate effect.

I checked the stats in MPC HC, and it shows a constant 8ms jitter.

So at least I know what's happening now.
Now if I could just find a way to make it play smoothly...