Mix sugar, paprika, garlic powder, onion powder, cumin, cayenne, and 1/2 tsp.salt in a bowl. Using a fork, prick pork all over. rub sugar mixture over pork. wrap tightly in plastic wrap, and refrigerate for 8 to 24 hours. Unwrap pork and place in slow cooker.
Spread barbecue sauce evenly over pork, cover and cook til pork is tender, 9 to 11 hours on low or 5 to 7 hours on high. Transfer pork to large bowl, let cool slightly then shred into bite size pieces, discarding excess fat. Cover to keep warm. Let braising liquid settle for 5 minutes. Remove fat from surface using large spoon.Season with salt and pepper. sugar and vinegar to taste.
Toss shredded pork with 1 cup braising liquid. Add more liquid as needed to keep meat moist. Serve with barbecue sauce.