In a small bowl, combine salt, black pepper, and garlic powder. Set aside.
Cut pork butt or pork shoulder roast into pieces that fit into your sous vide machine. If it fits in your plastic bag and the cooker, then leave it whole.
Take a sharp knife, and score the fat cap in a cross-hatched pattern.
Rub the seasoning blend all over the pork on all sides, massaging it as you go.
Place the seasoned meat into a freezer zip-lock bag or a vacuum bag.
Seal appropriately using either a vacuum sealer or the water displacement method.
Set sous vide cooker to 165 degrees F, and cook for 24 hours. Be sure to submerge the sous vide bag completely in the water. See notes for tips and tricks below for this method.
Remove from the sous vide, and immediately place in an ice bath until cold.
At this point, either place in the refrigerator for up to 5 days or finish immediately, as follows.
Cut the bag open, and save the gelatinous liquid for later in the refrigerator.
Place the meat in a smoker, and smoke around 200 degrees F for 2 - 3 hours.
Heat the juices from the bag until hot.
Shred the pulled pork using shredding claws or two forks into bite-sized pieces. If desired, place the meat back into the hot juices to keep the pulled pork moist and hot.
Serve as is, on a bun, or topped with your favorite BBQ sauce.