well a manual would have given you engine braking which an auto can't

Not so. I had good engine braking via lockup in all three gears. Hardly touched the brakes in 2 days. Never looked like losing control despite road grades that are well beyond what you would find in the west. Other complication is many of the downhill sections have speed bumps every hundred yards and they are strictly walking pace bumps.

Yes, lot of autos have no lockup in first, but the F350 seems to have it, and down to a very low speed as well.

Agreed....years ago i wouldn't of dreamed of having an Auto...now after 2 years into a 5 year trip in an Auto i would never want a Manual..so much easier off-road..in sand..rocky terrain etc etc...just drop it into a low gear as you would a manual and hold it there if you have to. Just stop and go pedals.
Would always choose a Auto now..as was said though..if it went wrong i would be buggered.

I prefer manual at all times, unless it's city driving with a lot of stop & go on hills.