Mmmm jerky...lol Got this from tops
Is that a 2.5 lbs with or without the fat cap? I typically remove the whole fat cap. and smoke it straight up with apple wood. I wouldn't go with anything more harsh than Oak wood.
Anyhow, for medium, take it the tri-tip to about 140-145 degrees, smoking between 230 - 250 degrees. If you peak at 170 or so, don't panic, just let the temp drop. It should only take 2.5 - 3 hours to get there.
If you want the tri-tip to be real tender (nice pull-apart) take it to 150-155 degrees. 3-3.5 hours is all it should take.
Keep your rub simple. I try not to put too much salt. Pepper, Kosher salt, and garlic make a nice tasting tri-tip.