go to
http://www.jamminproducts.com/setups.htm and check out chad bradley's version 2 standard setup. it works very well for me on varying tracks. macnkitty also has hit the nail on the head i believe with there not being enough dampening (too light a shock oil) to slow down the rebound and compression speed of the shock because of the heavy spring you're using (the blue ofna big bore spring is the heaviest one out of the 3, red is medium and yellow is soft). a question for you: are you on the throttle through these bumps you're having trouble with? if so, you may want to go to less anti-squat...that will allow the rear end to absorb bumps better when you're on the throttle. good luck!