Prepare the Pork - Trim the excess fat from the pork shoulder. Cut into four pieces. Transfer the pork pieces to a 6-quart slow cooker.
Make the Barbecue Sauce - In a medium bowl, whisk together tomato paste, pineapple juice, maple syrup, molasses, mustard, paprika, garlic powder, chili powder, onion powder, and salt. Pour the barbecue sauce over the pork, turning to coat the pieces.
Cook the Pork - Cover and cook until pork is very tender and easy to separate with a fork, 5 to 7 hours on the "High" setting, or 8 to 10 hours on the "Low" setting.
Shred the Meat - Transfer the pork to a sheet pan or bowl and shred it into smaller pieces. Cover with foil to keep warm.
Degrease the Sauce - Use a spoon to skim and remove the excess fat from the surface of the sauce. The sauce can also be transferred to a fat separator or bowl to remove the grease.
Reduce the Sauce - Add the defatted sauce to a large saucepan. Bring to a boil over medium-high heat. Cook the sauce, stirring occasionally, until thickened and reduced to about 1 ½ cups, 15 to 20 minutes. Season sauce with salt and pepper to taste.
To Serve - Transfer the shredded pork to the slow cooker and combine it with 1 cup of sauce. Serve the remaining sauce on the side with the pulled pork.
Notes
Using Bone-in Pork: If using bone-in pork shoulder or pork butt, purchase a 7 to 8-pound cut to account for the weight of the bone.
Storing: Store cooled pork in an airtight container in the refrigerator for up to 5 days.
Reheating: Cover and microwave in 15 to 30-second increments until hot.
Freezing: Place in a resealable plastic bag for up to 4 months.