Smoked my first tri tip on the BGE yesterday.
They are not a common cut in the South and not often encountered at the grocery store counter, but what a wonderful cut of meat done on the grill!
I put a rub similar to what I put on Boston butts and smoked over hickory then reverse seared it. Tender and flavorful. I've been missing out.
I discovered this cut about 6 months ago, and it is a favorite of ours now. Like you said....slow smoked to about 125*, reverse sear to 135*, a wonderful medium rare treat. You may ask your butcher, but an even better tri-tip is called a Pecanha roast. It is a sirloin cut with a fat cap. It is wonderful.