In case anyone was wondering, I got this fixed by my own fiddling. I still don't know why it was running too fast. It could just be because it's such a low end table. I got it running just a little bit over 33.3 by adding strips of duct tape to the underside of the platter where the belt meets it. This changed the gear ratio ever so slightly, and I'm please with the result. I can tell, by comparing it to a digital recording, that it's still running a tiny too fast, but it's good enough for my purposes.