Season the pork with garlic powder, salt and pepper; place into a 4 to 6 quart pressure cooker. Fill with enough water to cover. Close the lid and bring up to 15 pounds of pressure. Cook for 1 hour. Release the pressure and drain off juices, reserving about 2 cups. Shred the pork and mix with barbeque sauce, adding reserved liquid if needed to reach your desired consistency.