I have cooked Tri-tip many different ways. I have smoked for two hours at 180, panned and foiled for three more hours at 250. This way turns out very tender, juicy and tasty. That being said I now prefer to Smoke for one hour, then crank to high and BBQ until you get an IT of 130. Let set 15 minutes, slice against the grain and enjoy one of the best cuts of meat, in my opinion.
I love me some tri-tip, enjoy.