Sprinkle tri-tip with kosher salt. Massage Chipotle Rub into meat. Let steak sit at room temperature for 1 hour or refrigerate uncovered overnight. Bring to room temperature before grilling.
Build a two-zone fire in a charcoal grill, or preheat a gas grill to medium-high. Cook 3–4 minutes per side over direct heat until nicely charred. Transfer to low-heat side (or lower gas grill heat to medium) and cook an additional 6–8 minutes per side or until an instant-read thermometer registers 120°F for rare (steak will carry over to 125°F, or medium-rare, as it rests).
Transfer meat to a carving board; let rest for 10 minutes. Thinly slice against the grain.
Prepare Chipolte Rub
Grind 1 1/2 stemmed, seeded, chopped dried chipotle chiles in a spice mill; transfer to a small bowl. Grind 2 tablespoons pink peppercorns, 2 tablespoons coriander seeds, 1 teaspoon fennel seeds, and 1/4 teaspoon cumin seeds in the same spice mill; transfer to bowl with chiles. Stir in 2 teaspoons dark brown sugar, 2 teaspoons kosher salt, and 1 teaspoon mustard powder