4 low

Driving roads the likes of which I have not driven in years and never in a Jeep, I have a question for more experienced drivers. I have a 2005 X, automatic with a 4.0L I6, all stock drive train. The roads I am running now are usually very rocky and have a lot of grades, some quite steep. The...

I'm well aware that 4 Low must be engaged when at a complete stop or barely rolling. However, I have heard some people say that while 4 High can be engaged at speed, you should never engage it at speeds over 35 mph. Is this true? If so, what's the reasoning for this?