When I'm grilling a tri-tip, I tend to just spray the roast down with olive oil, and rub it with Pappy's seasoning. I leave that covered on the counter for an hour or so to take the chill off the roast, then grill it to medium rare, rest, and slice.
When I smoke tri-tip, I treat it more like brisket (minus the injection). When shopping for the tri-tip to smoke, I try to find the most marbled piece in the cold case, which makes for a much more tender and flavorful end product.
I rub mine down the night before with the Obie-cue Bigbull's Texas Brisket rub. The next day, I smoke over pecan @250 degrees - occasionally spritzing with apple juice and makers mark, and adding more rub.
Once the roast hits about 135-140 degrees, I crank up the smoker to 350 for about 10-20 minutes, then pull and double wrap in foil for a rest (in a cooler, wrapped in towels) until ready to serve. I serve it thinly sliced 1/8"-1/4" thick.
Total time, 2 1/2 - 3 hours.
Here's a shot of the last tri-tip I smoked up:
Edited by rocapps - 6/20/10 at 2:09pm