When you say skipping frames, is this during playback, and when you rendered what kind of file did you make? If it's a quicktime, you can check to see if it's skipping frames by using your arrow keys and go through the video frame by frame or just bring your rendered file back into AE and see if all the frames are there. If they are it's most likely a playback issue with your CPU(rendered files can often be way too large to play correctly on a computer).
See this from adobe:
: Why is my output file huge, and why doesn't it play back smoothly in a me...
Johnny Cuevas, Editor
Thinkck.com
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.
