Ahhhh.....Tri-Tip was my first love. I was so enamored with it that I threw away my gas grill and bought a Santa Maria BBQ Outfitters Grill. Santa Maria, California is where the whole thing started. If you've never seen a SM Grill, google it. I have probably cooked well over 1,000 lbs of Tri-Tip now (I'm only 35) and I feel like I have mastered it. It's a common meat here in California, and I just payed $8.49 lb for Prime here at a local Costco this weekend. The choice was $7.49, so it was a no brainer to get the Prime. If you ever have a chance to get Prime Tri-Tip - do it! Tri Tip can be tough if not cooked correctly. You have to pull it under 140 at least. I pull at 125 because medium rare Tri-Tip is a food of the God's. It finishes around 130 - 133 typically. Then the other key - SLICE ACROSS THE GRAIN!!! I've seen so many YouTube Videos of people just slicing it length wise. NO! The grain changes somewhere near the middle. Cut it in half where the grain changes, then slice accordingly.
As far as a rub goes, you really can't go wrong. S&P, Onion, & Garlic. To be a traditionalist, you add dried parsley - but not necessary, just pretty when it's raw.
Fellow Brethren, The Rub Co. from here in CA, have a Santa Maria Rub that will knock your sox off! I definitely recommend getting some from them.
To me the 2 very finest things in life, are a perfectly cooked Prime Tri-Tip, and now my newest obsession, a perfectly smoked Brisket. Amen.