To make adobo sauce: combine vinegar, lime juice, chipotles, garlic, cumin, oregano, black pepper, salt and cloves in a blender or processor on high speed until smooth.
Cut roast into about 12 large pieces.
Pour oil into large skillet and sear all sides over medium-high heat until browned.
Place meat into slow cooker and pour adobo sauce over meat.
Cook on high heat for 6 hours or on low for up to 10 hours.
Remove meat from slow cooker and shred with two forks. Place in bowl and add liquid in ½ cup amounts from slow cooker to meat until meat is moist. Discard any remaining liquid and place meat back in slow cooker on low heat. Serve on corn tortillas, if desired.