Been to Busters quite a few times (Mom and Dad live up there in St Helena). I like my tri-tip with rosemary, OO, minced garlic, salt, pepper and a little oregano. Grill it over a high heat for a nice herb crust and finish indirect with oak smoke - but the "real deal" (the original from Bob Schutz at the Safeway meat department in Santa Maria) just had garlic salt and pepper on it and was done on the rotisserie. Any way you cook it, you gotta serve it up with ranch style beans, garlic bread and a little pico de gallo relish.
And in Santa Maria they do these "En Masse" and rotate the skewers by hand. This is what Northern California BBQ is all about!