Then there's fine tuning the engine...
(Carb. adjustment, timing adjustment, rebuild the engine, etc.)
Also, I rebuilt my SM420 trans. and just turning it by hand you can really feel the huge frictional losses through the transmission. I've also got a later 350 automatic trans. sitting around that had much less friction. Everyone's is different, though. You can also check your brakes to make sure they're not rubbing too much while disengaged.
