Place the onions and garlic in an even layer in the slow cooker and pour in the stock. Combine the sugar, chili powder, salt, cumin, and cinnamon in a bowl. Pat the pork dry with paper towels. Rub the spice mixture all over the pork and place the meat on top of the onions and garlic. Cover and cook until pork is fork tender, about 6 to 8 hours on high, or 8 to 10 hours on low. I

Turn off the slow cooker and remove the pork to a cutting board. Strain onion mixture over a bowl and return solids to slow cooker. Set strained liquid.

Remove bone if there is one. Using 2 forks, shred meat to bite size pieces, discarding large pieces of fat, return the shredded meat to the slow cooker, add BBQ sauce, and mix. If you're not using BBQ sauce, use a spoon to skim and discard fat from the surface of the strained cooking liquid, and then add 1/4 cup of the liquid at a time to the slow cooker until the pork is moistened. Season with salt as needed.