1. In a skillet, toast the dried guajillo and ancho peppers until fragrant, then soak them in hot water for 15 minutes.
2. In a blender, combine the soaked peppers, onion, garlic, cumin, oregano, and a cup of beef broth. Blend until smooth.
3. Place the beef chuck roast in the slow cooker and pour the blended sauce over it.
4. Add the remaining beef broth, salt, and pepper to the slow cooker.
5. Cook on low for 8 hours or until the meat is tender and easily shredded.
6. Once cooked, shred the beef and serve in tortillas with chopped cilantro and lime wedges.

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