In a Dutch oven, brown roast in oil. Combine tomatoes, chiles, taco seasoning, bouillon and sugar; pour over the roast. Cover and simmer 2 to 2-1/2 hours or until meat is tender.
Remove roast to a platter and keep warm. For gravy, pour 2 cups pan juices into a saucepan. Combine cold water and flour; stir into pan juices over high heat until thickened and bubbly, about 3 minutes. Serve with roast. Freeze option: Place sliced pot roast in freezer containers; top with gravy. Cool and freeze. To use, partially thaw in refrigerator overnight. Microwave, covered, on high in a microwave-safe dish until heated through, gently stirring; add a little water if necessary.