Hello! I saw your post from a few years ago. I have an 89 4runner, 3.0 6cyl 3vze engine. The automatic transmission was doing similar to what you have described. Not engaging when I first started it up. When I revved it up for a minute it would finally engage. What wound up being the problem with yours. The shop says I need a new transmission but I don't know how extensively they checked it. Any help would be appreciated.
Thanks,
John