The thing about Tri-Tip is it's shape allows for you to please everyone. It will be more done on the ends then in the center if grilled over high heat. You can end up with medium rare in the thick center and medium to medium well at the thinner ends.
Also you can slice it early and bring out some slices to finish on the grill for that invited guest who does not eat any meat under medium.
The Trisket that Jack is speaking of is pretty simple to make. Start the tri-tip out at 225F until the IT reaches 140F then tightly wrap in foil and bump up the temp to 260F until the IT of the Tri-tip hits 195F to 200F. This typically takes around 5 1/2 hours. Then let it rest for at least 30 minutes then slice across the grain using Jack's slicing diagram.
It comes out super moist and tender. You can slice it and it does not fall apart. Give it a try one time.
Does this look dry?
Slices like butter but does not fall apart.