Preheat your Yoder Smokers YS640 pellet grill to 250ºF, set up for smoking. Also, install your GrillGrates to preheat for the finishing sear.
Trim any excess fat and silver skin from the outside of the tri-tip.
Combine the seasonings and mix well. Apply a thin layer of oil to the roast. Coat all sides with the rub. Let rest 5-10 minutes.
Smoke the tri-tip on the second shelf of the grill until the internal temperature reaches 110ºF. Remove from the grill, and cover loosely with foil.
While the tri-tip is smoking, make the Three Hots Horseradish Sauce. Start by whipping the heavy cream to soft peaks. In a separate bowl combine the mayo, horseradish, House of Q Slow Smoke Gold and Melinda’s XXXTra Original Habanero Pepper Hot Sauce and whisk to combine. Then, using a spatula, gently fold in the whipped cream. Season with salt and pepper.
Increase the temperature to 500ºF, and remove the door from your two piece diffuser (or remove the entire diffuser). Replace the grates, with the GrillGrates directly over the fire box.
When the grill comes up to temperature, grill the tri-tip on both sides to achieve grill marks and color. Remove the roast from the cooker when the internal temperature reaches 125ºF.