Thanks for comments everybody!
You don't need the Carnet de Passage for any countries in Central or South America, and we have never been asked. A temporary vehicle import permit is issued at the borders.
The only "vehicle document" we have arranged before starting the trip (Central and South that is, USA is a different story for a European vehicle....) is insurance. We use a Dutch company called Alessi, and they provide liability and comprehensive for Central and South America. However, 5 countries (Mexico, Belize, Nicaragua, Costa Rica, and Colombia) does not recognice forreign insurances, and it is mandatory to purchase this locallly at the border when you drive in. The comprehensive part is valid though.
Regarding acclimatization to higher altitude, this is normally not a problem as you climb gradually higher and higher. Most people will be fine driving from sealevel and up to about 3000 meter (9000 ft) without getting altitude sickness. You'll probably feel it, but only as being out of breath when moving around. Driving up into the Andes from Colombia, you climb and camp gradually higher and higher (with some days driving back down). Going from Colombia and into Ecuador, you will be fairly welll aclimatized before finding the really high mountain passes.
As a rule of thumb, you normally try to not increase the sleeping height more than 300 meters (900 ft) every day above 3000 meters (9000 ft), and every fourth day should be a "rest" day (not climbing higher). When aclimatized, going back down to sealevel for a couple of days, maybe as much as a week, would normally not be a problem. However, how a human body responds to altitude can be very different, and you should always be careful. It is also much less critical to drive over a high pass and being exposed to high altitude for a relatively short periode of time, compared to actually spend the night there. So if you can sleep at 3500 meters (11500 ft), it would not be a problem driving over a pass at 4500-5000 meters (14-15000 ft) for a couple of hours as long as you go back down before setting up camp.
So, yes! We do feel the altitude when going over the high passes, or when we camp high up inthe mountains, but it has never been a problem.
E
