Any ideas how to slow this thing down?

Try slowing your feed rate and lowering your expectations.

Both good ideas.
But if I told you I had a solution to your speed problem for about
$20, would you be interested? The only solution I see is to get an
appropriate blade. I bet your 28 tpi blade is fine for cutting 1/4"
ply, but for anything thicker than that, call Iturra designs
(866-883-8064) and get a real blade. Or suffolk machinery (http://
http://www.suffolkmachinery.com/sili...el_pricing.asp) or any other place
that will weld up a blade to your length, if you can't find a
replacement blade at HD. Really not trying to flame here, but why are
you willing to fight with a speed control and whatever else, when it
sounds like you know the real solution?
Good luck,
Andy