Barbecue Beef Sandwiches

5 tablespoons dark brown sugar, divided
3/4 teaspoon black pepper
2 1 pound flank steaks
1 cup chopped onion
1 cup tomato paste
3 tablespoons Worcestershire sauce
3 tablespoons molasses
3 tablespoons cider vinegar
1 tablespoon chili powder
1 teaspoon garlic powder
1 teaspoon dry mustard
1 teaspoon ground cumin
1/2 teaspoon salt
10 2.5 ounce submarine rolls, halved
red onion slices, optional
dill pickle slices, optional

Combine 1 tablespoon brown sugar and pepper; rub over both sides of steaks.

Combine 1/4 cup brown sugar, onion and next 9 ingredients 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.