I think I remember seeing in the manual 55, but that may have been the top speed to engage 4H. If the conditions require 4WD, probably should not be going that fast anyway.
80km/h or less (50mph) to engage into 4Hi, after that you can drive as fast as you want once you are engaged. There is no speed limit once you are engaged.
you don't want to use 4H on dry pavement for the 5th gen. it has a locked center differential. The 4th gen 4runners, you can use it on 4H unlocked on dry pavement.