Make marinade: Combine 1/2 cup oil, 1/2 cup lemon juice, 1/4 cup brown sugar, 1/4 cup white sugar, 2 Tablespoons soy sauce, 2 Tablespoons kosher salt, 1 1/2 Tablespoons black pepper, 3 cloves minced garlic and 1/2 teaspoon onion powder in a blender. Mix well.
Marinate the beef: Add tri tip to zip top bag and pour marinade over top. Close top, and put in the refrigerator for at least 8 hours, or overnight.
For the Grill: Preheat the grill too 500°F. Sear each side for 3 minutes. Lower the grill to about 400°. Cook in closed grill for 20 minutes, then flip and cook on other side for another 15-20 minutes. Cook until desired temperature. 125 - 130 for rare, 135 - 140 for medium and 145 - 150 for well done
For the Smoker: set the smoker to 225°F and smoke the tri tip for 2.5 - 3 hours, or until it hits 130°F. Sear it on the grill over medium high heat for 5 minutes on each side to caramelize the outside
Rest: Remove tri tip from grill and place on rimmed pan or cutting board. Allow to rest for 10 minutes before slicing. Slice against the grain and serve warm.