A general rule of thumb to follow when driving in mountainous areas with a two-speed rear axle... Columbia or otherwise..
The gear range required to go up the hill, is the same gear range used to go down the hill.
Columbia's and generally speaking any two-speed rear axle, will shift to the low range on an up hill pull, if the shift is made before the engine is "lugging", once the engine is allowed to lug, vacuum is lost, as is the ability to shift the rear axle...
In the mid to late '60's, large trucks with two-speed rear axles went to an electric shift system, in lieu of vacuum...
Anytime a vehicle that is equipped with an OD is being driven in mountainous areas, this includes modern cars/SUV's, the trans/diff should be shifted out of OD before down hill travel is encountered.
The OD transmissions that Ford used starting in '49 worked great for light trailer pulling, that is if the operator took the time to read the owners manual.. The manual advised that the OD feature should be dis-engaged in mountainous areas and when pulling a trailer... This guideline is still true on the late model vehicles..