Heat grill. On 24x18-inch sheet of heavy-duty foil, combine potatoes and carrots; drizzle with 3 tablespoons orange juice concentrate. Sprinkle with thyme and salt. Wrap packet securely using double-fold seals, allowing room for heat expansion.
Meanwhile, cut pork tenderloin lengthwise, cutting almost to but not through bottom. Open tenderloin; press to flatten slightly. Brush both sides of pork with 2 teaspoons orange juice concentrate. Sprinkle both sides with pepper.
When ready to grill, place foil packet on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Cook 10 minutes.
Turn packet over; place pork on grill. Cook 7 minutes. Turn pork; cook an additional 4 to 6 minutes or until pork is no longer pink in center and vegetables are tender. Open packet carefully to allow steam to escape.
To serve, cut pork into slices; serve with vegetables.