In a small bowl, mix salt, black pepper, dried thyme, dried rosemary, minced garlic, onion powder, dried oregano, and smoked paprika. Rub the spice mix evenly over the tri-tip roast.: The spice mix should look evenly combined, a dusty mosaic of red and green flecks that smell fragrant when you bring the bowl close. As you rub the mixture into the tri tip , press firmly so the rub adheres and creates a thin crust that will brown slightly as it cooks slowly. You should notice the perfume of garlic , the piney note of rosemary , and the warm sweetness of smoked paprika all at once. This contact between seasoning and meat is crucial because the long cook time draws those flavors inward; if the rub sits for even 10 to 15 minutes, it starts to penetrate the surface. A frequent misstep is applying too little pressure or not spreading the rub uniformly, which leads to uneven seasoning where some bites taste muted. If your rub feels damp, pat it dry with a paper towel and re apply so it clings rather than sliding off.
Place the seasoned tri-tip into the slow cooker. Carefully pour beef broth and Worcestershire sauce around the meat to keep the seasoning intact.: When lowering the roast into the cooker, you want to avoid disturbing the seasoned surface, so tilt and nestle it gently. Pouring the beef broth and Worcestershire sauce around the edges, rather than straight onto the top, preserves that seasoning crust while still providing the moisture needed for connective tissue to break down. You will hear a soft wet sound as the liquid settles, and steam will begin to rise as the cooker warms. This liquid acts like a flavor reservoir, bathing the meat and concentrating as it reduces; without it the roast can dry at the exposed top. A common oversight is adding the liquid on top which makes the rub slide off and dilutes the concentrated flavors.
Cover the slow cooker and set it on low for 6-7 hours, or until the meat is tender and easily shreds with a fork.: As the cooker warms, you will notice a gentle, building aroma in the kitchen that shifts from the sharpness of raw garlic to a rounder, savory stew like scent. The long low heat allows collagen in the tri tip to convert into gelatin, giving the meat that melt in your mouth texture. Resist the urge to lift the lid often, because every peek releases heat and lengthens cooking time; only check in the final hour. A telltale sign of readiness is when the meat yields easily to a fork and the edges appear frayed, glossy from the rendered juices. If after the stated time it still resists shredding, continue to cook in 30 minute increments, as undercooking is the most common mistake here.
Remove the tri-tip from the slow cooker and shred it using two forks. For a sandwich option, lightly butter and toast buns, layer with shredded meat, and top with a slice of Swiss cheese; place under a broiler just until the cheese melts. Serve with a small bowl of the strained cooking liquid as a dipping sauce if desired.: When you lift the roast from the cooker, it should come away in large, tender pieces that pull apart with little effort. The texture is glossy and moist, and the aroma is intensified when you shred, releasing the concentrated juices. Shredding with two forks creates irregular strands that trap sauce and melt slightly when paired with toasted buns. For the sandwich finishing, the tiny sizzle as buttered buns hit the pan is a sensory cue that the bread is crisping properly, while the brief broil to melt the Swiss cheese should be watched carefully because cheese can go from oozy to scorched in seconds. Straining the cooking liquid removes solids and gives you a silky dipping sauce, which elevates each bite by adding moistened richness. A common error is letting the shredded meat sit too long without moisture, which can make it seem dry; reserve some liquid and toss gently before serving.