I feel your pain. Very frustrating! I'm assuming you have 19.5" wheels? There are good alignment shops out there, just few and far between when it comes to your specific vehicle/chassis combination. Some Ford Truck dealers are better than others. IMO, all you can do is keep calling around in your locale until you find someone who is familiar with your vehicle.
IME, increasing the air pressure in your front tires (above 80 psi recommended) will help with the outer edge tire wear, but, as others have said, will compromise ride quality. (smoothness/harshness) I use 85-90 psi in my 30' Class A F-53. If possible, moving some rear axle weight forward may help a little with directional stability. If still no joy, increasing the caster and getting the toe-in right will make it seem like a different vehicle.
You don't state the current mileage. If over +=60,000 miles, you might want to consider replacing the shocks.
Chum lee
