In the slow cooker, combine the apple juice, sugar, soy sauce,vinegar, ginger, garlic powder, salt and pepper. Add the roast and turn to coat with the apple juice mixture. Ensure pork is fat side up.
Cover and cook on LOW for 6 to 8 hours or until fork tender.
Remove the roast from the slow cooker and place in on a platter. Cover it with foil to keep warm. Strain the cooking liquids from the slow cooker into a small saucepan, skim fat if necessary. Bring to a boil.
Combine the water and cornstarch to make a paste.
Stir the cornstarch mixture into the boiling liquid. Cook, stirring, until thickened, 3 to 5 minutes.