Video Playback Stuttering

Hey guys, I'm hoping you'll be able to help me with a problem that I've been having. I feel like I've tried everything to no avail.

My Setup:
Windows 7 x64
K-Lite Mega
Q6600 2.4GHz
eVGA GTX 460
Samsung LNA650
Video via mini-HDMI to HDMI (secondary extended display)
Audio via Optical

Now my problem is that video playback on my TV has an occasional stutter, like it is out of sync. I have tried playback in MPC-HC, Boxee and XBMC with and without syncing the display resolution and even setting in the nVidia control panel, my TV to both 23, 24 and 60Hz and I still see the same problem. Now I bought this video card hoping it would solve the problem as my previous card was an 8800GTX and the hardware acceleration works flawlessly... when playing back on my main LCD computer monitor (An old Acer 1440x1050), but as soon as I send the video to my Sammy It starts dropping frames.

I am at my wits end, because It happens with all HD video I send at it whether is H264, VC1 or x264 (all in MKV containers made with mkvmerge). I just don't understand because when I start playing a video in MPC-HC, it starts in my main monitor and I can see it playing back butter-smooth, then I click to fullscreen it on my Sammy and about every 10 seconds there is a little bit of slowdown/jitter. I even just tried it with a 480p MP4 file and I see the same thing. Also I have almost all extra settings turned off on my TV, especially AutoMotion Plus and I have the input to "Just Scan".

Please help me, I can't stand it any more

Thanks for the responses.

I was thinking of doing a clean install of my OS. But I don't know how that will help solve my problem because as I said, when a video is playing on my main monitor it plays back perfectly, with 0-2% CPU usage on high-bitrate 1080p. As soon as I send it my TV then is starts lagging (but still only 0-2% CPU usage), I'm thinking it has to do with how my TV is processing the input signal rather than how my computer is outputting.

Thanks you so much for that suggestion. Set Vsync to forced in global setting and I think it pretty much solved it. Just watched a 2 hour movie and noticed a little slowdown, but not anywhere near as often as before. I had my display set to 60Hz so it maybe have been the pulldown. I have now set my display to 23Hz and I hope that is the end of my problems.

Thanks so much for the help guys!