Trim excess fat from the roast and cut into 8 large pieces. Pat dry and season liberally with salt and pepper.
Add vegetable oil to a large, heavy pan, and heat over MED-HIGH heat. Once oil is shimmering, add half the meat to the pan, leaving room in between each piece. Let meat sear on one side without moving it for several minutes. If you try to flip the meat and it sticks to the pan, let it cook a little bit longer. It will release on it's own when it's ready to flip.
Sear all sides of the meat, remove to a plate, and repeat with remaining half of meat.
Add all meat pieces to the bottom of slow cooker, making sure to add any drippings from the plate, that's extra flavor!
Add vinegar, garlic, cumin, oregano, cloves, pepper, salt, beef stock, lime juice and chipotle chiles to a blender and puree until smooth. Stir in drained green chiles.
Pour sauce over meat in slow cooker, turn to fully coat meat in the sauce, then add bay leaves.
Cover, and cook on LOW for 10 hours (or HIGH for 6 hours).
Remove bay leaves.
Remove meat to a large bowl and shred. Return meat to the slow cooker and heat on LOW in the sauce, uncovered, for 10 minutes.