Your pistons and rings might be worn out. You might want to rebuild your motor. Depending on snow condidtions, you may get 10,000 miles on a set of hyfax, or a few miles. Even so, you should replace them at least once a year. And concerning a suspension upgrade, I think the FAST M-10 would fit in your sled.
!997 Polaris Storm 800
1.5" Lug Track