First of all, I would have a separate drive for editing. Leave "C" for operating system/programs only.

Second, preview is just that - preview. It is not final - just enough to get the job done. So, don't preview in BEST. Preview in PREVIEW Auto. Best is for taking a frame for a still shot.

Render your "problem" area. If the jitter is still there - forget everything I said. If it's gone, you don't have a problem.

Dave