I have never had a one way in the spur set up that slipped, it sounds to me like maybe you got oil inside the clutch bell, and its not allowing the clutch shoes to fully engage the the clutch bell. If the one way slips at all the truck wouldnt move, yet the first post stated that the truck would barely move. I would check the inside of the clutch bell, clean it out and scar it up with some medium grit sand paper, should fix you right up.