Combine 3 tablespoons brown sugar, onion, and next 6 ingredients in a 3 1/2-quart electric slow cooker; stir well. Combine remaining tablespoon brown sugar, pepper, and salt; rub pork roast with sugar mixture. Cut pork roast into 4 large pieces; add to slow cooker, turning to coat with sauce. Cover with lid; cook on high-heat setting 1 hour.
Reduce heat setting to low; cook 7 hours or until pork roast is tender. Remove pork roast from slow cooker, reserving sauce in cooker.
Shred pork roast with 2 forks. Return shredded pork to slow cooker, and stir well to coat with sauce. Spoon 2/3 cup pork mixture on bottom half of each bun, using a slotted spoon. Cover with tops of buns.
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