You basically need mountain trained units for tasks like that. For example the Italians in WWI/WWII had special alpine units which had lighter weight equipment. In China the issue is even larger since those are the tallest mountains in the world. So even oxygen deprivation might become an issue. You need training camps where troops can get used to the 4000m altitude's oxygen levels and get drilled on how to survive in that sort of terrain before you even consider operations. They should have a detached unit structure for that specific terrain which is able to make their own equipment purchase choices. This should include clothes and even weapons. Some weapons might have issues with low-oxygen or freezing conditions. Other weapons, like high caliber cannon, might not be transportable.