I have a 99 summit w/ gade track, and the start of this winter on ice, it would go 105, at the end of the year, about april 29th, on ice (moosehead Lake) It would go about 85, do you think the motors going or what?

Belt is shot.

belt and you should probably clean your clutches surprising the difference that will make

Check your compression first if that is good get a new belt and rebuild the clutches.

check the belt first and clean the clutches with compressed air. My mxz does lose top speed and out of the hole performance when the belt is worn very little. If the track tension is to tight that will decrease top speed also, just be careful not to run it to loose if it is studded because of track ballooning and geting into the heat exchangers. My mxz600 zx chassis with good belt runs 100-105 on the lake. Goodwin clutches, fett brothers reed stuffers, boyesen reeds and jetting it down on the mains really made the sled come alive.