They should go 300+k plus with no major issues besides normal wear parts as long as normal maintenance is performed. They really need no maintenance besides filter changes until 100k.
The normal wear parts are.
- Alternator
- Belts
- Brakes
- Suspension (shocks, bushings, springs, tie rods)
- Tires
With a high mileage truck... over 100k. I would avoid KDSS (only on some trail editions). It may last much longer (maybe 200+k) but the cost to replace is too risky (IMHO) if you start ownership over 100k. It could be removed, but it would require fabrication skills and expensive parts.
Overall. they are one of the most reliable platforms out there..Simple and outdated.. but designed to take a beating. However, the parts are very expensive when things do go wrong. The more basic the truck... the better off you will be with higher miles. 2wd is better for overall reliability.. but if you need 4wd they are also very reliable, just quite a few more things to go wrong. Avoid sunroof at all cost on an older one. Probably the most problematic area of a 4runner.