1. Heat oven to 350 degrees F.
2. In a small bowl, mix preserves, mustard, vinegar, garlic salt and pepper. Place roast, fat side up, on a rack in a large roasting pan. Spread about 2/3 of the glaze all over roast.
3. Bake roast at 350 degrees F for 45 minutes; brush on remaining glaze and roast another 35 to 40 minutes or until internal temperature reaches 150 degrees F on an instant-read thermometer.
4. Cover meat loosely with foil and let rest for at least 15 minutes. Internal temperature will rise to 160 degrees F. Cut into very thin slices and serve.