The key to cooking short ribs so they are tender & juicy is for the meat & tissues to break down. The low & slow cooking on a wood, pellet, or electric smoker does the job well. The main reason your ribs may not be tender is that they did NOT cook long enough. Many think they are well-done and overcooked but that is likely not the case. Continue cooking the short ribs until the meat pulls away from the bones. The internal meat temperature should be 205°.