Welcome to the forums! Glad you've joined us. You've found a great place to learn and share ideas on smoking, grilling and curing great food! There are lots of friendly and knowledgeable people here who really enjoy helping one another. Just ask any time you need help and you'll get plenty!
Good luck with that sirloin tip roast! Using the 3-2-1 method on a roast is a new one on me. That method is normally done with pork spare ribs, so I'll be interested in seeing how that turns out. You can always browse through some threads of other members who've smoke sirloin tip:
Be sure to show and tell us how it turns out!