: I've tried...
: - making sure I'm not pushing on the blade;
: - trying to make the blade go faster/slower;
: - trying a new blade;
: - trying a more coarse blade (I'm using "fast sheet
: metal" blades for a nice clean cut);

I'm no expert, but have you tried using a wood blade? When I was cutting forms, like you I thought I'd use a metal blade because I assumed the finer teeth would give a smoother finish. In fact, I found I wavered and the much larger toothed wood blade gave a much better result. Admittedly I was using MDF not ply, but perhaps he same might be true for you?

Cheers Ian