Root beer gives these slow cooked pork sandwiches rich color and pleasant sweetness.
Trim fat from meat. If necessary, cut roast to fit into a 3-1/2- to 5-quart crockery cooker. Sprinkle meat with the salt and pepper. In a large skillet brown meat on all sides in hot oil. Drain off fat. Transfer meat to cooker. Add onions, the 1 cup root beer, and garlic.
Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours.
Meanwhile, for sauce, in a medium saucepan combine the 3 cups of root beer and the chili sauce. Bring to boiling; reduce heat. Boil gently, uncovered, stirring occasionally, about 30 minutes or until mixture is reduced to 2 cups. Add root beer concentrate and bottled hot pepper sauce, if desired.
Transfer roast to a cutting board or serving platter. Using a slotted spoon, remove onions from cooking juices and place on serving platter. Discard juices. Using 2 forks, pull meat apart into shreds. To serve, line buns with lettuce leaves and tomato slices, if desired. Add meat and onions; spoon on sauce.
Do not substitute with diet root beer.