Dropping frames/stuttering playback on FCP timeline

I'm experiencing stuttering playback when playing 1920x1080 mov file video from the FCP 7 timeline.
I never had this problem before and haven't done anything new that I can see. files are from a JVC HM 700 pro HD camera.

When the space bar is hit, video plays fine then once every 10-15 secs the video "sticks" for a half of a second then plays fine then repeats the "stick"

if I go to finder and play the mov file using quicktime it plays flawlessly smooth. Obviously it's a performance issue with my drives or FCP 7 overhead not keeping up with the playback rate stream.
I can ocasioanally close down FCP and reopen and it will be fine for an hour then get fussy again holding on frames. My drives are Seagate Baracuda 7200RPM 32cache

Are these dropped frames? What are some things I can try or do to isolate/diagnose the problem or fix it? Help greatly appreciated!

Thank you,

Bob Accettullo

Steve,

Thank you for the reply. It's possible transcoding to pro res would make FCP happier. Funny thing I can work for hours with smooth playback, then I might check something online using Safari and come back to FCP and the timeline playback starts to stutter and jerk every 5 secs or so. Restarting the Mac Pro will usually clear this for a while until it starts stutering again. Seems like a system performance thing, strange.
Used to NOT do this, same files, changed nothing.

Bob