As of August 2015, Traeger Wood Pellet Grills features two recipes for prime rib. One recipe involves a dry rub and roasting directly on the grill. The other recipe involves marinating and roasting on a rack.
For a pan-roasted prime rib with sauce, tie a 6-pound roast at 2-inch intervals with butcher's string, and place in a large, resealable plastic bag. Make a marinade combining 5 cloves garlic, 2 tablespoons red wine vinegar, 1/2 cup chopped parsley and 2 tablespoons fresh rosemary in a blender or food processor with 1/2 cup olive oil or vegetable oil until the mixture is well-blended. Cover the roast with the herb mixture, and marinate for two hours at room temperature. Remove the roast from the marinade, and liberally season on all sides with Traeger Prime Rib Rub. Place the roast, fat-side up, in a V-shaped rack in a roasting pan. Pour 2 cups beef broth into the bottom of the pan.
With the lid open, set the grill to smoke for about five minutes, or until a flame is established. Close the lid, and preheat to 450 F. Place the pan with the prime rib onto the grill grate, and roast for 30 minutes. Reduce the temperature to 250 F, and continue cooking until the desired wellness is reached, approximately two to three hours. Wellness is determined by the internal temperature of the roast, at least 130 F for rare. Transfer the roast to a cutting board, and let rest, loosely covered with foil, for 20 minutes.
To make a jus, pour the drippings into a small saucepan, and skim off any fat that rises to the top. Taste the jus, and season to taste. Carve the roast into 3/4-inch slices, and serve with the jus.