scrolling judder

I tried using the scrolling feature in fcpx with credits and it plays back very jerkily. I set the edit mode to Better Performance and it didn't make any difference. Someone told me that it exports OK, but it doesn't seem to. I bought Ripple Tools II hoping their scrolling feature would be better, but I get the same thing. Has anyone run into this before?

thx

What are your project settings, and what is the duration of the scrolling credits clip?

1080P, 24. The credits rolled for about 25 seconds. I managed to get it to play back much better. It may have been as simple as the way I had the window sized - who knows, but it's fine now. Thanks.

For what its worth, I like using theTrebuchet font group for scrolling text. particularly the bold looks nice (not too bold) and holds up to scrolling well in all sizes.