If the motor revs fine and feels strong its probly the clutch. Pull off the flighting and take the gear case and clutch assembly out for an inspection. Might have oil or grease on the clutch and its slipping or the springs are binding. Might as well repack the gear case with decent low temp grease too. The factory grease in a lot of augers sucks period. My Z51 would hardly turn the flighting in really cold weather with the OEM muck in the gear case.
