Can you please mention some more details like:-
1.Premiere pro version
4. Graphic card in the machine
5. is it dropping frames, how is it behaving ?
Do they jump when played in the camera?
Did you ever solve this issue?
Can you give us more info?
Have you tried lowering the resolution on the playback? Is it on Full? I've got a pretty quick computer but it often lags when I'm playing back on anything over 1/2.