Combine the garlic powder, curry powder, 1 tablespoon of the brown sugar, chili powder, allspice and black pepper in a medium mixing bowl. Reserve 1 tablespoon of the spice mix; rub the remaining spice mix all over the pork. Wrap the pork in plastic wrap and refrigerate over night.
Heat oil in a large skillet over medium high heat. Add the pork and cook, turning to brown on all sides, this should take about 20 minutes. Transfer to a 4 to 5 quart slow cooker.
In a small bowl, mix together the vinegar, the reserved tablespoon of the spice mix, the remaining 3 tablespoons brown sugar, sweet and sour sauce, Worcestershire sauce, hot pepper sauce, liquid smoke, dry mustard, cayenne pepper, chopped onion and minced garlic. Pour mixture over pork in crock pot. Add 1/3 cup water or apple juice to drippings in skillet, with a wooden spoon stir to loosen up any particles in bottom of pan, pour water/juice mixture over pork in crock pot.
Cover and cook on low for 6 to 10 hours or until pork is fork tender. Remove pork from crock- pot, shred pork using two forks. Return shredded pork to crock-pot. Stir pork into juices in crock-pot. Heat on high for 1 to 2 hours.