1Place pork in large resealable plastic bag set in a shallow dish.
In a small bowl, whisk together balsamic, oil, rosemary, garlic, pepper & salt; mix well & pour over meat in bag. Seal bag; turn to coat pork. Marinate in the refrigerator for at least 1 hour (or more), turning the bag occasionally.
3Remove pork from marinade, discarding marinade. Prepare grill for indirect grilling. Test for medium heat about the drip pan. Place tenderloin on grill rack over drip pan. Cover & grill about 40 minutes or until an instant read thermometer inserted in center of the meat registers 155 degrees F.
4Meanwhile while meat is cooking make the glaze. In a small saucepan, bring balsamic to boiling. Reduce heat; simmer, uncovered, for 5 minutes. Makes about 1/4 C.
5Brush tenderloin on all sides with glaze. Grill for 1 minute more. Remove from grill. Cover with foil; let stand for 15 minutes (the meats temp will rise 5 degrees during standing time). Garnish with thyme. Slice to serve.