You'll have to give it a squeeze to see if it's thawed out.
I'd do a reverse sear. Smoke at 250ish till internal temp hits 110-115, then toss onto a hot fire to sear the outside. Remove from heat no later than 130, I prefer 125. Then rest it loosely tented for 15 minutes or so before slicing. If you don't rest it, all the juices will end up on the cutting board, instead of staying in the meat.
IMO, the worst thing you can do with a tri tip is try to cook it like a brisket. Med rare at the very most. Even medium is too well done for me on this cut. Remember, the temp will continue to rise during the rest period, so don't make the mistake of cooking it to 135-140, then being disappointed when it's overcooked on slicing.
Speaking of slicing, the grain changes direction in the middle of the meat, so you have to pay attention when cutting. Here is a nice video that explains how to carve a tri tip.