Cook garlic in oil in small skillet over medium heat, 2-3 minutes or until fragrant. Remove from heat.
Stir in vinegar, ketchup, worcestershire sauce, sugar and basil.
Slash fat edges of roast and pierce both sides all over with a fork.
Place meat in plastic bag. Pour marinade over meat.
Refrigerator overnight (10-24 hours), turning several times if possible.
Drain meat, reserving marinade and dividing.
Grill over medium coals or at medium heat on your gas grill for 25 minutes, brushing with marinade.
Turn, grilling 20-25 minutes more or until desired temperature is reached.
Heat remaining marinade and serve with sliced roast. Can also be served with chimichurri sauce.