Combine 1 tablespoon brown sugar and pepper; rub over both sides of steaks. Combine 1/4 cup brown sugar, onion, and next 9 ingredients (onion through salt) in an electric slow cooker. Add steaks; turn to coat. Cover with lid; cook on high-heat setting for 1 hour. Reduce heat setting to low; cook for 7 hours. Remove steaks; reserve sauce. Shred steaks with 2 forks. Return shredded steak to cooker; stir into sauce. Spoon 1/2 cup steak mixture onto bottom half of each roll; top with onion and pickles, if desired. Cover with tops of rolls.