Mix all dry ingredients in small bowl to make a rub.
Trim any leftover silver skin or fat from the roast.
Sprinkle meat with rub and massage lightly all over. Cover and refrigerate at least an hour or as long as overnight. Remove from refrigerator an hour before cooking.
Prepare a charcoal grill or heat a gas grill to medium. Place roast on grill and sear one side well, 4 to 6 minutes, checking for flare-ups. Turn the roast and sear on the other side for about the same time. Then lower gas to low or move the meat to a cooler part of the charcoal grill.
Turn meat again and cook another 8 to 10 minutes. Flip and cook again. A 2-pound roast will require about 15 to 20 minutes total cooking time. The roast is ready when an instant-read thermometer reaches 125 degrees when inserted into the thickest part of the meat.
Preheat oven to 300 F. Roast Tri-Tip on a rack in a roasting pan until internal temperature reaches 125 degrees when inserted into the thickest part of the meat.
Rest roast on a cutting board 10 to 20 minutes. Slice against the grain. The roast is shaped like a boomerang, so either cut it in half at the center of the angle or slice against the grain on one side, turn the roast and slice against the grain on the other side.