Rub the tri-tip roast on all sides with the salt, pepper, and garlic powder. Let it sit at room temperature for 15 minutes so the flavors can settle.
In a small saucepan, combine the olive oil, butter, and BBQ sauce. Warm the mixture gently until well blended to create a basting sauce.
Place the tri-tip on the cooler, indirect heat side of the grill. Grill for about 20 minutes, turning every 5-7 minutes. Baste with the warmed sauce after each flip to keep the meat moist.