If you are running the spool, you are probably missing teeth on the front belt too. If you hit anything, and the tires stop turning, the weakest link is going to give. The teeth on the side belt, or front belt are going to strip off if hit hard enough. I would try going to the front diff with 100,000 fluid and see if that helps from stripping the belt before looking into different pullies or anything else.
Am I going back racing?...Hmmm.. Not anytime soon... But soon enough.