Place the ham, flat side down, into the bowl of a large slow cooker. Sprinkle the brown sugar, salt and pepper on top and rub it into the ham. Pour in the pineapple juice and maple syrup. Arrange the pineapple slices on top and on the sides of the ham. Cook on high for 3 to 5 hours or on low for 6 to 8 hours. Baste the ham every half hour to prevent drying.
Allow to cool slightly on a platter before cutting and serving.