Combine hoisin, vinegar, soy, garlic and sesame oil in a small bowl. Place the tenderloin in a medium shallow baking dish, pour over the marinade and marinate in the refrigerator 3 to 4 hours or overnight, turning once. Preheat the grill. Remove the pork from the marinade, removing any excess. Season with salt and pepper and grill 10 to 12 minutes for medium doneness.