I've got 152k on my 03 V8 Limited 4Runner. The biggest issue that I've had is frame rust. My frame was swiss cheese. Toyota just replaced my frame (my cost: $2k), but they did that under "goodwill". There has been no frame recall. As a result, each instance is being independently reviewed. Toyota is replacing some frames but other people are simply being told that their truck is out of warranty.
So if you are buying a used 4Runner, get it up on a lift and take a good look at the frame, particularly the cross member under the transmission.
The other recurring problem I've had is frozen calipers. I've replaced front calipers at least 3 times and rears at least twice.
Check the transfer case for leaks. Sometimes an o-ring can flatten around the actuator. While the problem is a cheap o-ring, as I understand it the Toyota authorized fix is over $1k.
My V8 has been great. Early V6s are having issues intake manifold leaks, IIRC. The fix is very expensive.
If the 4Runner you are looking at has the XREAS crosslinked shocks, have them checked carefully. Replacing them with new XREAS shocks is prohibitively expensive (around $3k). Most just replace them with conventional shocks when they wear out.