Preparation In a small bowl, mix together the brown sugar, paprika, chili powder, cumin, salt and pepper. Rub the mixture all over the pork pieces. In the pressure cooker, whisk together the cider vinegar, water, ketchup and liquid smoke. Add the apple slices. Add the pork pieces into the pot. Seal the lid, and bring the pressure cooker up to high pressure over medium-high heat. When the cooker reaches high pressure, lower the heat to medium-low or lower, and cook for 45 minutes. If needed, adjust the heat to keep at high pressure. Remove the pressure cooker from the heat and allow it to sit with the lid still locked for 15 minute to naturally release the pressure. After 15 minutes, quick release any remaining pressure. Remove the lid and place the pork to a large bowl. Return the pressure cooker to the stove without the lid. Skim off any fat from the top of the sauce in the cooker. Bring to a boil and simmer until the sauce has thickened and reduced to approximately 2 cups, 10 to 15 minutes. When the pork is cool enough to handle, shred into bite-sized pieces. Pour 1 cup of the sauce over the pork, and serve the rest on the side. You may also serve with your favorite barbecue sauce. Spoon the pork onto the buns and serve.