check this
You probably have a lot of preload in the front shock of the rear suspension also. Without you sitting on the sled, back the preload off on this shock until the spring just barely wiggles around loosely then give it one full turn of preload. set the preload on the rear shock at 2.5" - 3.0" and the preload on the front shocks at about 2.0" - 2.5". I personally also set my limiter straps so that there's about 1.00" - 1.25" of bolt sticking through the jamb nut which give me a lot of ski pressure.
I have a '99 SX 600 updated with Viper shocks and all the other parts to make it a long travel sled so mine is pretty close to your chassis. One other thing, if the back end is wanting to pass you from entry to the apex of a corner you may want to think about putting 96 studs down the center of your track to help with braking traction entering the corner and rear end tracking as you transition around the corners.
Mills