Combine marinade ingredients: large bottle of Italian dressing, ¼ cup Worcestershire sauce, 4 Tablespoons brown sugar, 1 Tablespoon minced garlic, 1 teaspoon red pepper, 1 teaspoon black pepper, and 1 teaspoon onion powder
Put tenderloins and marinade in a sealed container or ziptop bag. Marinate at least 30 minutes up to 24 hours; rotating occasionally. Grill over a medium fire (350 degrees) 5 to 6 minutes rotating once then another 5 to 6 minutes on the second side. Check meat, when a meat thermometer registers 145°F at the thickest portion it is done. Remove tenderloin and allow to rest before cutting. Serve with the following sauce.
SAUCE
Combine the brown sugar, white vinegar, chili powder, black pepper, red pepper, garlic powder, and Worcestershire sauce in a saucepan. Whisk to combine.
Heat the sauce ingredients just until it begins to boil. Turn the heat off and allow to sit until the meat is ready. You can pour over tenderloins or serve in a bowl for dipping.