Toss some peaches on your still-hot grill for a sweet, refreshing meal.
In bowl, whisk first 3 ingredients for sauce. Coat each tenderloin with 1 tbsp. oil and 1 tbsp. brown sugar; season. Grill pork, covered, over medium-high heat, turning often, until centers register 145° on instant-read thermometer, about 15 minutes. Brush peaches with remaining 2 tbsp. oil; grill, cut-side down and covered, until grill marks form, about 5 minutes. Serve pork and peaches with sauce.