Preheat grill for indirect cooking over medium heat. Sprinkle pork loin with pepper and garlic salt. Place on grill and book about 1 1/2 to 2 hours or until internal temperature reaches 155-160 degrees. Allow meat to cool while preparing sauce. Shred pork into small pieces discarding any remaining fat. Place pork in large pot and stir sauce into pork. Simmer for 40 minutes. Serve on warmed rolls.
For sauce: heat butter in large saucepan. Add onion and stir frequently until softened, about 5 minutes. Add remaining ingredients and simmer for 30 minutes.