I'm only responding since no others have yet. I say that because I am a newbie myself and have no real solutions yet, just ideas to try.
I had a similar problem at one point in a video I was making. It was at the very end where I had the credits start rolling. There was a whole mess of things going on at that very second when it switched to the credits and my preview of the video would hang up. I would have to manually advance the preview about a second to get past that part and it would continue.
I was worried it would translate to the produced video, but once I produced it, there was no glitch or jump to be found. I'm guessing it was because of the power or lack thereof of my computer.
Have you tried to produce the video and see if the finished product has these same glitches in them.
Also, I am recommending with and issue like this, to post your DxDiag along with your question. You will find you will get a lot more helpful responses when people have all the information they need to give you a quality response. The problem could be caused by lots of things and the pro's that frequent the forums are of great help when they have all the info.
Good luck! Let us know if the finished project has these issues!
-Max