Rub tri-tip roast with olive oil and then garlic and herb dry rub. Using injector inject the roast in at least 4 spots with the butter/garlic sauce. Plug each hole with the first chile and then the garlic. Let stand for at least an hour (2 hrs preferred).
Light gas grill and set on low to medium flame. Place wood chips in foil on flame and place roast on second rack or highest rack available fat side down. Slow roast the tri-tip for 20 to 30 minutes or until desired doneness, not turning it for the whole time it is being roasted.
Remove when done and serve immediately.