Soak the wood chips in water at least 1 hour; drain.
Combine sugar and the next 4 ingredients (through 1 1/2 teaspoons salt) in a bowl. Pat pork dry, and rub with sugar mixture.
Remove grill rack, and set aside. Prepare the grill for indirect grilling, heating one side to high and leaving one side with no heat. Pierce bottom of a disposable aluminum foil pan several times with the tip of a knife. Place pan on heat element on heated side of grill; add 1 1/2 cups wood chips to pan. Place another disposable aluminum foil pan (do not pierce pan) on unheated side of grill. Pour 2 cups water in pan. Let chips stand for 15 minutes or until smoking; reduce heat to medium. Maintain temperature at 300°. Place grill rack on grill. Place pork on grill rack over unheated side. Close lid cook for 6 hours at 300° or until a meat thermometer registers 195°, covering pork loosely with foil after 5 hours. Drain and add 1 cup additional wood chips every 45 minutes. Refill water pan and add charcoal to fire as needed. Remove pork from grill; let stand 20 minutes. Unwrap pork; trim and discard fat. Shred pork.
Heat oil in a medium saucepan over medium heat; swirl to coat. Add onion; cook for 2 minutes, stirring frequently. Add 1/3 cup sugar and the next 5 ingredients (through 1/2 teaspoon salt); bring to a simmer. Cook 15 minutes or until thickened. Arrange about 3 ounces pork and 2 tablespoons sauce on each bun.