Typing dreadfully unresponsive in X.8

I've been waiting to install Mountain Lion on my late 2011 2.2GHz Quad-core i7 until I was certain that my most important software would run efficiently. So, yesterday I finally did my full backup and installed X.8 with updates. Everything went picture perfectly. All my apps work fine so far except for some Ambrosia software, but I was expecting that, so no worries. I have noticed one aggravation, though. I do quarterly newsletters for an NGO in Pages. I have done them for years. I began one last week under the Lion OS and everything was perfectly fine as it always has been. Now, when I go to work on the same newsletter (very same file) in Pages under Mountain Lion, the typing is horridly unresponsive. I type and it takes a second or better for the text to show up. I can literally be halfway through a line of text before it appears in the document. Everything looks fine, but the lag is utterly distracting.

I've checked my activity log and I'm not even using half of the 8GB of RAM installed, so I don't think it would be a memory issue. And in all other apps the typing works just fine (including Safari right now that I'm running with the Pages document open). What's even more confusing to me is that if I open a new document with a blank page, the responsiveness is normal there as well.

Now the newsletters are pretty graphic intensive, but that's never caused any issues before.

Does anyone know what could be causing the problem and possibly have a solution?

Many thanks!