it happen to me on my impulse nytro last year....i has a bolt loose on the fuel pump cover and mist of snow was going in the tank and gas was freezing up a bit.......check for a leak on the fuel system......if same problem, your fuel regulator might freeze up too and crack the diaphragms so not enough fuel when boost coming therefore running like crap once sensing boost.
my sled was inside a garage all the time and after 20 minutes riding if i stopped for 5 minutes, then i could ear my fuel pump coming very loud(gas starting to freeze in my fuel line)
in your case, maybe the fuel pump is going bad simply??
hope this help.......
