Thanks to the Cyber Film School, I've identified why it is I've bogged down in the screenplay a bit. This article talks about how writing a screenplay is much more "bare bones" than writing other sorts of fiction. With this in mind, I see that much of the "outlining" that I've been doing is, in fact, moving the screenplay forward. I maybe need a few more snapshots to fill out my vision, but I don't need a lot more description. The details come in production, not in writing the screenplay.