You might take a look at all the threads dealing with loss of power and superchargers, etc. There is a lot that has already been covered on the forum. I had a similar problem with my '09 RXT late last summer/early fall. Folks were kind enough to help after I had sifted through a lot of the stuff--and eventually I found a busted hose between the charger and throttle body. Mind you, I had been working on the ski for two weeks, replaced plugs, done compression tests, taken it for diagnostics at a local dealer, etc. Didn't find my little problem until MUCH, much later. It turned my SC'd beast into a naturally aspirated one with similar speeds and RPMs to the ones you have listed. I am no expert--but there are tons on here--I would simply take a while to read up. I did and gained a ton of valuable knowledge about my ski in the process. I think you will be well-served to look at the loss of power/speed/thrust type posts. You may find the answer much quicker, but regardless, your search won't be in vain.