If the butcher has not already done so, tie the roast at 1-1/2 inch intervals with butcher's string.
Season the roast generously on all sides (including the ends) with Traeger Prime Rib Rub.
When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes). Put a large cast iron skillet on the grill grate. Set the temperature to High and preheat, lid closed, for 15 to 20 minutes.
Add the vegetable oil to the skillet.
Put the roast in the skillet and sear on all sides, turning with tongs. Don't forget to sear the ends, too.
Transfer the roast directly to the grill grate and carefully remove the skillet from the grill. (It will be very hot, so put it in a place where no one will touch it accidentally, such as in your oven, which of course, you never use anymore.)
Reduce the temperature of the Traeger by selecting the """"Smoke"""" setting on your thermostat. You can leave the grill lid open for a few minutes to hasten the cooling.
Roast the meat for 3 to 3-1/2 hours, or until the internal temperature in the thickest part of the meat is 135F when read on an instant-read meat thermometer.
Let the meat cool to room temperature, then cover tightly with aluminum foil or plastic wrap. Chill for several hours, or overnight. Remove the butcher string.
Slice the roast very thinly, preferably on a meat slicer, and use to build your favorite roast beef sandwich.