Rub dressing mix evenly over roast. Inject butter sauce evenly into roast. Wrap tightly with plastic wrap, and place in a shallow dish or large zip-top plastic freezer bag; cover or seal and chill 8 hours. Let stand at room temperature 30 minutes before grilling. Remove plastic wrap.
Light one side of grill, heating to high heat (400° to 500°); leave other side unlit. Place roast, fat side up, over unlit side of grill, and grill, covered with grill lid, 3 1/2 to 4 1/2 hours or until meat thermometer inserted into thickest portion registers 185°. (Meat will easily pull away from bone.) Let stand 15 minutes. Coarsely chop, and serve with Ranch-Barbecue Sauce. Garnish, if desired.
Note: For testing purposes only, we used Cajun Injector Creole Butter Injectable Marinade.