I'll try a shot at this one:
Drew, I think your helix has too steep of finish.
JyST?? You mentioned you do lake riding. Us both being from WI, you probably have hardly any snow. Enough to cool heat exchangers but maybe slides are getting hot and starting to stick to track at that speed. Are you sitting on gas tank when you let off gas? Anything smell funny? Had similar issue with Cat tonight. Lake was pretty much bare ice and sled ran worse and worse and got a smell like burning rubber, almost belt like but different. I couldnt get past 80 then. I told GF we should go home before Cat falls apart, but she was having so much fun on SRX that it took some convincing. Got to boat launch and had to cross street, I did and looked back and she had handlebar turned and smashed into curb. I ran over and helped it over curb as cars were coming. Got sled up and then the red and blues started flashing. I got in argument with warden and cop was talking to GF(They were hiding in boat launch to nab drunk sledders). I quit drinking 7 months ago and she never did so they tried everything to bust us for something. Anyway. when we finally left, The arctic cat fired right up and rode smooth and free. Thats why I asked about lake. Yami never did this just arctic cat. but you never know...
Hope I helped
P.S. TRY not to argue with conservation wardens!