Put roast in a zip to lock bag. Combine remaining ingredients and add to the bag. Seal and marinate in the refrigerator for 1 hour, turning after 30 minutes.
Heat gas grill on high.
Sear the tri tip for 5-7 minutes a side.
Turn the heat to medium and cook for 25-30 minutes, turning a few times, until internal temperature reaches 140 degrees Fahrenheit.
Remove from heat, cover with a tent of aluminum foil and allow to rest for 10 minute
Cut roast in half where the meat grain changes direction. Slice each half thinly.
Notes
To bake in an oven instead of grilling:
preheat oven to 350 degrees
in a large ovenproof skillet, heat a few tablespoons of olive oil
sear both sides of the tri tip, about 3-4 minutes a side
roast in the oven about 10 minutes a pound until instant read thermometer reads 140 degrees