This has nothing to do with speed at which I am shifting it. Fast or slow, it grinds. I have owned this truck for 16 years and have shifted it in and out of four-wheel-drive who knows how many thousands of times. It didn’t do this before.To keep it from grinding you need to move the lever fast(er).
As soon as your TC moves into Neutral the input shaft spins up just by the drag forces inside the AT and that causes the TC to grind going into gear again. This can be avoided by moving the lever quick.
Another way is to have the AT in P for the shift so nothing moves and you have all the time of the world to do the shift.