So im curious as to why you're ripping half the powertrain apart for some minor clunking. If it bothers you that much then carry on. All my GM vehicles clunk and for the same reason - minor amt of built-in longitudinal slip yoke travel between the trans/t case and yoke.None at all just the clunking when releasing the throttle like I’m going to coast or when I go to reverse. I had a slight vibration around 50 but that was because I put my driveshaft in the wrong way I flipped it and it went away.
Not saying yours is that but not saying it isn't either...