My landcruiser is intermitentely losing power and discharging white smoke

You may have a bad head gasket. The white smoke might be coolant that is seeping into the combusiton chamber and making it hard to ignite the air/fuel charge and thusly reduces power. If you can, take a smell of the exhaust and see if it smells sweet like anti-freeze or if it smells like burnt oil. In either case it is probably a bad head gasket or if it is a burnt oil smell it could also be that the valve stem seals are bad and creating the same issue in the combustion chanber.

I am giving you a link to a diagnostic walk through that will go into more depth on these possibilities, go over others and help you find the most likely source of the problem. They are very well put together.

Here is the link;

https://www.2carpros.com/articles/white-smoke-or-steam-coming-from-the-exhaust-pipe