Slow-cooked Barbecue Beef Sandwiches

Description
Purchased from the Bowers Estate in Fort Worth, Texas in 1994. Date and source unknown. This is marked as a family favorite. I have tried these and they are good.
 * Contributed by Cat's Recipes Y-Group

Ingredients

 * 3 pound rump roast, trimmed
 * 1 tablespoon beef bouillon
 * 3 tablespoons flour
 * 1½ teaspoons chili powder
 * 15 ounces tomato sauce
 * 1 clove garlic chopped fine
 * ½ cup white onion, chopped
 * 1 teaspoon dry mustard
 * ⅓ cup brown sugar packed
 * hamburger buns
 * 2 tablespoon lemon juice

Directions

 * 1) Rub flour into roast.
 * 2) Place in bottom of crock-pot and add remaining ingredients except buns.
 * 3) Cook on low for 14 hours.
 * 4) Serve over buns.