In a medium mixing bowl, COMBINE first 6 ingredients; SET aside.
SPRINKLE roast with salt and pepper.
In a large Dutch oven, HEAT oil over medium-high heat; BROWN roast on all sides; TRANSFER roast to a 5 1/2-quart slow cooker.
Pour tomatoes and chili mixture over roast; COVER; COOK on high until meat shreds easily with a fork, about 5 to 6 hours.
REMOVE roast from cooker; CUT into large chunks; KEEP warm.
SKIM fat from liquid in slow cooker.
MASH about 2/3 of the pinto beans; ADD to slow cooker; STIR until combined with juices.
STIR in black beans and remaining pinto beans; RETURN roast chunks to cooker; COOK on high an additional 25 minutes.
Garnish each serving with one or more of the suggested toppings
1. We use Ro-Tel brand. 2. Original recipe suggests using "eye of round." May also substitute pork tenderloin.
Per Serving (excluding unknown items): 5558 Calories; 34g Fat (5.4% calories from fat); 365g Protein; 978g Carbohydrate; 331g Dietary Fiber; 110mg Cholesterol; 821mg Sodium. Exchanges: 63 Grain(Starch); 23 Lean Meat; 4 Vegetable; 1 Fat.