Preheat the smoker to 250 degrees F. Remove the Picanha from the refrigerator and trim the fat and silverskin off of the top of the roast. You don’t have to get every bit of fat, just the majority of the cap so it doesn’t shrink and toughen during cooking.
Pat the meat dry and apply your favorite rub to both sides. Place the meat in the smoker in a central position that isn’t too close to the heat. Cook for about 2 to 3 hours, spritzing with a mix of water and apple cider vinegar every 20 to 40 minutes. Aim for only 4 to 5 spritzes in total, spread evenly throughout the cooking period.
Smoke until the meat reaches an internal temperature of 130 degrees F. Take it off the smoke and wrap it tightly in aluminum foil or butcher paper. Let it rest in an empty cooler for 45 minutes to finish cooking. Unwrap, slice, and serve immediately.