Braising Liquids: Combine the orange juice, lemon juice, white vinegar and pour into the slow cooker.
Create the Rub: Mix all of the dry spices with the olive oil.
Apply the Rub: With your hands lightly knead the rub into the surface of the chuck roast (or rib roast). Place the roast in the braising liquid.
Slow Cook: Cover and cook on low for 7-8 hours for best results. Cooking the meat low and slow will create a beef that is incredibly tender and easily shreds with a fork. For faster results, set the slow cooker to high for 4-5 hours.
Shred and Serve: Once cooked, remove the beef from the slow cooker and shred it using two forks. Return the shredded beef to the cooking liquid, stirring to coat. The beef will absorb even more flavor this way.