Grilled Beef Tri-Tip Roast & Potato Planks

Combine pepper and garlic. Press evenly onto all surfaces of beef roast. Toss potatoes with oil. Place roast in center of grid over medium, ash-covered coals. Grill tri-tip roast, uncovered, 35 to 45 minutes for medium rare to medium doneness, turning occasionally. Grill potatoes 20 to 25 minutes or until tender, turning frequently. Remove roast when instant-read thermometer registers 140°F for medium rare; 155°F for medium. Tent loosely with foil; let stand 10 minutes. Combine sour cream and pesto. Carve roast across the grain into thin slices. Season beef and potatoes with salt, as desired. Top potato planks with sour cream mixture; sprinkle with red peppers.