1) Post this in the competition forum. A few teams there that have done tri-tip in competition might point you in the right direction.
I did one in a backyard comp and I smoked it at 325 tell a it of 125, then pulled it and put in a foil pan of butter garlic and herbs that was about 160 and let it rest for 15 mins and finish getting it to 130-135. Turned in pencil slices from the widest part and it was by far the best tri-tip I have done... at home I grill over oak, or smoke, or even gas grill just don't over cook it