Preheat your Yoder Smokers YS640s Pellet Grill to 250ºF, set up with the diffuser door removed, a Yoder Smokers Reversible Griddle (raised ridges side up) over the fire box and the second shelf in place.
Trim any excess/hard fat from the surface of the rib roast, as well as any visible silver skin.
Rub the surface of the roast with the Kozlik’s Mustard Dijon Classique. Season with Cattleman’s Grill California Tri-Tip Seasoning.
Tie the roast with kitchen twine, about every 1” to allow the roast to hold its shape during the cooking process. Touch up any areas where the seasoning was disturbed on the surface.
Transfer the prime rib roast to the second shelf of the grill. Smoke at 250ºF until the internal temperature reaches 105ºF, about 2.5-3 hours. Remove from the grill. Cover with foil.
Increase the grill temperature to 500ºF and remove the second shelf.
The griddle should be very hot in about 15 minutes time. Keep your roast under foil and in a warm (or room temp) area to avoid losing too much heat.
Sear the prime rib roast on the griddle, turning to sear all sides. Continue cooking until the internal temperature reaches 120ºF in the thickest part of the roast, about 20-30 minutes. You can move the roast off of the griddle and to the indirect side of the grill if you need to bring the internal temperature up without adding any more sear to the surface.
Remove the roast from the grill. Cover with foil and rest 20 minutes before slicing to serve.