Combine the granulated sugar, pumpkin pie spice and cinnamon in a large zip-top bag or a medium bowl. Set aside.
Dip each ball into melted butter then toss into a freezer bag and shake everything together or dip each ball into bowl, coating well.
Place two pieces of paper towels to cover the slow cooker (this prevents condensation from dripping) then place lid carefully over the paper towel and cook on high for 1-1/2 - 2 hours. (**VERY IMPORTANT: If your slow cooker runs hot, check at 1 hour then again at 1 1/2 hours to be safe.)