Add chuck roast to slow cooker. Combine remaining shredded beef ingredients in a bowl and pour evenly over top of roast. Secure lid and cook on low for 10 hours (high for 5hours).
In the last 30 minutes of cook time, remove lid. Remove bones (if present), then use tongs to pull and shred the meat. Mix back into the sauce and re-secure lid for remainder of cook time.
In a sauce pan over medium heat, add pinto beans, tomatoes, cumin and chili powder. Stir to combine and let simmer until beef is ready.
Lay tortilla out on flat surface. Add a portion of beans, topped with shredded beef. Next add cheese, lettuce and then sour cream. Fold in the sides of the tortilla first. Then roll up from the bottom to the top.