Finally got my first ride in today. My sled has developed a bog at different RPM's. On the stand it runs great through the RPM band. On the snow it boggs out at varying/random RPM's. If i feather the throttle I can get it up to the full 8k RPM, but otherwise it can barely hit 7k. It seems like it wants to go but just wont "shift out". It seems to run OK when cold, but after a mile or so it just wont pull revs anymore. Any ideas? I'm guessing in the clutch but no idea where to start.