I provide an update on the 4L60E that had the 3-4 neutral condition shortly after I rebuilt it. In this video, I bring in all the transmission components that would be involved directly or indirectly in such a failure, methodically test and evaluate each. I then get into the actual cause of the failure, which may surprise you.
Here's the video showing this transmission's tear down upon it arriving back at my shop: https://youtu.be/8XTGJqv_HRE