In a large dutch oven heat the oil over high heat. Salt and pepper the meat on both sides and then sear it in the dutch oven for about 4 minutes on each side. Remove and set into your slow cooker. To the slow cooker, add the onions, garlic and all the spices along with the vinegar, water, tomatoes, chipotle peppers, bay leave and molasses. Mix everything around with a fork and make sure the meat is nestled under all the juices. Turn your slow cooked to low and let it work its magic for 10 hours.