In a bowl combine soy sauce, garlic, and black pepper. Trim excess fat from meat. Use a sharp knife to score top and bottom of roast in a diamond pattern, making cuts 1/4 inch deep. Rub garlic mixture evenly onto all sides of meat. Insert a meat thermometer near center of roast.
In a grill with a cover arrange preheated coals for indirect cooking. Test for medium-slow heat in center of grill where meat will cook. Place meat on a rack in a roasting pan on grill rack. Cover and grill for about 1 hour or until meat thermometer registers 155 degrees F.
Remove meat from grill to cutting board. Cover meat with foil; let stand 15 minutes before carving. (The meat's temperature will rise 5 degrees F during standing.)
Meanwhile, in a small bowl combine half of the chopped mango, all of the onion, brown sugar, banana pepper, lime peel, lime juice, and salt. Tear off a 24x18-inch piece of heavy foil. Fold in half to make a double thickness of foil that measures 18x12 inches. Spoon the mixture onto center of foil. Bring up two opposite edges of foil. Fold foil to enclose the mixture, leaving space for steam to build.
Place mango packet on rack of uncovered grill directly over medium coals for 10 minutes or until heated through. Remove from heat. Transfer grilled mango mixture to a medium bowl. Gently stir remaining chopped mango and the raspberries into the grilled mango mixture. Serve with pork and, if desired, lime wedges. Makes 6 servings.