Cut the tenderloin into 8 slices that are 1 inch thickness.
Sprinkle the both sides of each slice of pork generously with garlic, rosemary, salt, and pepper. Cover with Saran and let set in fridge until 20 minutes before cooking. 20 minutes before grilling, let the meat sit at room temperature.
Add the glaze ingredients to a sauce pan and bring to a boil. Remove from heat. Use half the sauce for brushing the pork while grilling and the other half as a side when serving.
Grilling the Tenderloin:
Grill meat with Indirect/Medium Heat, meaning if you have a three burner grill, put meat in center and only have the side burners on. Cook for 10 to 12 minutes on each side and glaze each side with the BBQ sauce after turning. Meat is done when internal temp is at least 145℉.
Let meat sit for 5 minutes before cutting into it.