PREPARATION:

1. Prepare grill for indirect cooking.
2. Place peppercorns in small resealable food storage bag. Squeeze out excess air; close bag securely. Pound peppercorns using flat side of meat mallet or rolling pin until cracked. Set aside.
3. Pat roast dry with paper towels. Combine mustard and garlic in small bowl; spread over top and sides of roast. Sprinkle pepper over mustard mixture.
4. Place roast, pepper-side up, on grid directly over drip pan. Grill, covered, over medium heat 1 hour to 1 hour 10 minutes for medium or until internal temperature reaches 135°F for medium rare or 150°F for medium when tested with meat thermometer inserted into the thickest part of roast, adding 4 to 9 briquets to both sides of the fire after 45 minutes to maintain medium heat.
5. Meanwhile, prepare Sour Cream Sauce. Cover; refrigerate until serving.
6. Transfer roast to cutting board; cover with foil. Let stand 10 to 15 minutes before carving. Internal temperature will continue to rise 5°F to 10°F during stand time. Serve with Sour Cream Sauce.