How is the Eco Boost in the western mountains?

I've always read that a trailers brakes should be capable of stopping the trailer and the trucks brakes capable of stopping the truck. In reality we have all seen brakes smoking on vehicles at the bottom of hills so either this is not true OR some people do not keep up on their trailers maintance.

I would think a modern trucks, built and sold to tow would be capable of decending any hill, within reason safely.