Combine the ingredients in a medium saucepan. Bring to a boil over medium heat; reduce heat and simmer until thickened, about 45 minutes. Divide the sauce between 2 bowls, and set aside.
PREPARE THE PORK:
Preheat the grill to medium heat. Season the pork with salt and pepper. Sear, turning to cook on all sides, 10 to 15 minutes. Brush with half of the barbecue sauce, turning frequently, until pork is thoroughly glazed, about 10 minutes more (a meat thermometer should read about 150°F). Set aside and let rest for 5 minutes. Carve crosswise, and serve with the remaining barbecue sauce.
Notes
If you are preparing this recipe as gluten-free, just be sure to use a brand of ketchup that is known to be GF.