I usually cook mine to 135o and let it rest (brings it to 140o - the negotiated tri-tip IT at our house). Sliced thin, it's "prit' near perfect."
I see you've already seasoned these but next time, for the "real deal" (the original Santa Maria style), try just using salt, pepper, and (granulated) garlic with red oak smoke if you can. It's kinda like brisket in that the beef tastes so good you don't need to "enhance" it much.