Update
Drove without rear d shaft
Learned 2 things
Front shaft is VERY UNHAPPY above 20 mph. Not a surprise. 4in lift, d60, 205, in a blazer. I'll have to do some shimming
No spin did not unlock going straight. Made the normal ratcheting when turning and such
Totally livable. Acting like it should
So it looks like vibes, even tho not felt Mite be the issue.
Gonna sort out the front first so I can get up more speed to really test it. Plus it's more straight forward of a fix. And less expensive lol
Thanks for your help and patience