2015 Indy 600 SP overheat

I bought this sled new a few years ago. Had it studded at the dealer and he also installed tunnel protectors. This machine has run hot ever since I have owned it. Removed the protectors in an attempt to cure the overheat problem. That did help some what. Yesterday while riding it, in good snow (a bit warm 35 degrees) and running and moderate speeds (25-50 mph) engine temp was fine 127-135 F. Got on a bumpy trail (slower speeds) with minimal snow cover and temp climbed to 194F and the warning light came on. My wife actually rides this sled and my 2017 Pro S runs at a consistent 124F but did climb to 136F on the same trail. The Indy has had this problem since new and I also had a 2014 that did the same thing.
Questions:
What thermostat is stock on these?
Would a lower temp thermostat help this?
What can be done to fix this?
Thanks to all in advance.
Mark

2015 Indy 600 SP overheat