I bought a Morton's of Omaha marinated tri-tip at Costco last week.
Egg'ed it up last night. Very, very good.
No special cooking technique. Held the egg about 450, put the tri-tip on a raised grid. Turned every 15 minutes. Cooking time was about 40 minutes. Rested for 15 minutes afterwards while I grilled some squash and broccoli.
The tri-tip was very tender and had a great flavor.
If you are a Costco afficionado, this one is highly recommended.