PREHEAT grill for indirect heat by heating one side of the grill to medium heat and leaving burners on the other side of grill turned off. Mix chili powder, pepper and garlic powder; rub evenly onto all sides of meat. Place on cool side of grill; cover with lid.
GRILL meat, without turning, 1 hour. When internal temperature of meat reaches 140ºF, brush meat with 1/4 cup of the barbecue sauce. Continue grilling, covered, 10 min. or until internal temperature reaches 150ºF. Transfer meat to carving board. Tent with foil. Let stand 10 min. or until internal temperature reaches 160ºF.
CUT meat across the grain into thin slices. Add to remaining 1/2 cup barbecue sauce in large bowl; toss to coat.