Too much secondary spring and helix. You are slipping in the primary at full throttle hitting the rev limiter. Lets see some pictures of your primary clutch faces.
Did you just put in the black/purple secondary spring and helix at the same time of the fix kit? Sounds to me like soft rev limiter. Too much secondary pressure and you are slipping in the primary early.
I went with TRS clutch kit for 19-46. Its listed on snowest forums and ordered the kit from Rogers Sports Center . Custom 46/32 helix, 120-200 secondary spring, stock primary spring and 62 ish gram lightning weights. The 10-62s or 10-60s will work if on a budget. This will allow you to...
Gear down with your C3 belt drive and you maybe close. Fine tune once you try it. I would be more concerned with keeping the skis on the ground. Maybe the KISS coupler or ARC is your next investment.