AE No longer renders Preview Playback - always staggered - help?

I'm not sure what setting I may have hit / changed by accident, and please forgive my lack of knowing the proper terms to describe my issue but put simply, normally when I play / preview a segment of my timeline, it will render slowly the FIRST time, and the top green line will slowly fill to SOLID.  Then the NEXT time, if I haven't changed anything that segment will play smooth in realtime.  

Now the green area is staggered aand everything outside it appears solid and I can never get smooth playback no matter what my resolution settings are, etc.  Any ideas?  I did clear out the memory cache.

Thanks