Tri Tip is traditionally grilled over direct coals like a large steak. It is not usually done low and slow. You want to sear it on all sides to seal in the juices and develop a good "bark" then move it off the direct heat and allow it to cook to about 135 for med rare inside. Pull it off at that point, let it rest a few min then slice cross grain. I have never done it in a smoker. I suppose you could smoke it for about an hour and then grill it.
http://www.lospadrescounty.net/et/smbbq.html I do mine on a Weber kettle this way. Arrange the coals on one side. I usually add some hickory chunks to the coals. Then I throw on a foil pouch of soaked chips. Wait until it starts to smoke, then put the steak directly over the coals and close the lid. Sear on each side for 6-7 min with the lid closed. Then move off the coals and close the lid. Continue applying smoke if you like as we have all heard it should be absorbed up to 140 deg. Moniter with an instant probe and pull at 135 for med. rare. I get plenty of smoke flavor this way and cooking time is usually max 30 min for three lb tri-tip.
