1. Make 1/2-inch-deep slits on outside of roast; stuff with garlic. Combine cumin and next 3 ingredients (through black pepper) in a small bowl. Place roast in a 3 1/2-quart electric slow cooker. Sprinkle pork on all sides with spice mixture.
2. Combine juices and chipotle chiles. Pour juice mixture over pork. Cover and cook on LOW for 8 hours or until pork is tender.
3. Remove pork from slow cooker; shred with 2 forks. Skim fat from cooking liquid. Combine shredded pork and 1/2 cup cooking liquid; toss well.
4. Spoon 1 1/2 ounces pork mixture onto each tortilla; top each with 1 1/2 teaspoons onion, 1 1/2 teaspoons salsa, and 1 1/2 teaspoons cilantro. Serve with lime wedges.