In a large bowl, whisk together the brown sugar, whiskey, soy sauce, onion, garlic, olive oil, chili paste, and black pepper. Add the tenderloins, making sure to coat in the marinade. Cover with plastic wrap and marinate at least one hour, up to overnight. You may need to rotate the pork in the marinade every 20 minutes or so if it is not fully submerged. You can also marinate it in a gallon zippered bag.

Preheat the smoker to 225°F. Place the tenderloins directly on the grates. Smoke for 2-3 hours until the internal temperature reaches at least 145°F, or to your desired doneness. Brush with the marinade every 30 minutes.

Let the pork rest 10 minutes before slicing and serving. While the pork is resting, add the remaining marinade to a small saucepot. Bring to a boil and boil 5 minutes, serve with the pork.