MIX sour cream and 1 Tbsp. of the marinade in small bowl; cover. Refrigerate until ready to use. Pour remaining marinade into large resealable plastic bag. Add steak; seal bag. Turn bag to evenly coat steak with marinade. Refrigerate at least 30 min. or overnight.
PREHEAT grill to medium heat. Remove steak from marinade; discard marinade. Grill steak 16 to 18 min. or until medium doneness (160°F), turning occasionally.
CUT steak into thin slices. Serve with tortillas, sour cream mixture, Pico de Gallo and cheese.