You are Hitting the Rev Limiter and need the Click down on the primary But really my guess is this only happens on the trail going in to the mountains on Hardpack When your at Altitude in Soft snow if it still happens the certainly click down but just don't hammer it on the trail riding in on...
I Have a 2011 154 Free ride I lan to convert to 174 Any day now the track is fairly fresh
and in good condition and if I sold it would get me motivated to install the 174