There is a general thread of info here.. don't cook it like a chicken! It's done when it hits 130. No, cooking to 145 won't help.
Personally I like reverse sear on the weber kettle. Start off at around 250-275 indirect till IT hits 115-120. Pull off cooker, stoke up fire for a few minutes, then toss on direct heat for couple minutes a side. Remove and rest for 30 minutes loosely tented under foil. The end result will be a perfectly cooked piece of meat that shows med rare from end to end and side to side.
*edit* The above video that shows how to properly carve a tri tip is golden. If you slice it with the grain, you won't get it(the nirvana).
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)