I have an SDP series C15. it has installed a jacobsen 340E jake. I have been told it's the wrong jake for that model engine. It engages when I release the throttle, however it growls a little but doesn't roar. and it's squeezes a little but doesn't grip. under any substantial load (meaning over 20k on deck and 70k gross) it doesn't slow me down until I drop at least 6 gears (13sp). and it barely slows me down any sized hill empty until I drop 2-3 gears. anyone have any ideas?