We had the same problem doing an AMC20 last year. It seemed that the more force that we applied, the more stubborn the axle was. Ultimately, what worked was, after soaking the bearing with penetrating oil, as Lumpy stated, was to get a couple of large screwdrivers or pry bars behind the backing plate, one on each side, and pry while someone else whacked the hub flange from behind. Once the axle starts to move, you might need to put a small block of wood under the pry bar to maintain leverage. After working on these axles for several hours, once we took this approach, the axles slid out in a matter of minutes. Pry only as much as will not distort the backing plate.