First off, whats your system look like... and also what is the font that you are using for the text? I know when I was tring to create some text using the BleedingCowboys text, (you should google that to see what I am talking about) there were so many artifacts going along with that font (dust, lines, things that make it look cool) that it slowed down the PA interface when opened as a plugin in After Effects to the point that it was taking forever for it to render one frame just for a preview.
IF this is your problem I suggest that you make sure you are in DRAFT 3D mode... also if you just got PA and you are trying to do text with lots of extra stuff on the font, that slows down and eats ram up because it has to render all of those individual peices.
I would say you could go two ways, find an easier font to work with... or bring it into illustrator, and do the make outlines function, delete the unneeded artifacts, save it as an .ai WITH COMPRESSION TURNED OFF, import as an illustrator file into PA.
Remember these are all situations with me assuming your situation.
Good luck and get back to me!
Topher Welsh
Head Editor & Motion Graphics
http://www.scout.com