Place the pork pieces evenly in the bottom of the slow cooker.
Layer the sliced apples, diced onion, and chopped celery over the pork.
In a mixing bowl, combine the stuffing mix, chicken broth, dried sage, salt, black pepper, and melted butter until the stuffing is moistened.
Spread the stuffing mixture over the top of the apples and vegetables.
Cover and cook on low for 6 to 8 hours, until the pork is fork-tender and the stuffing has absorbed the flavors.