Vibrations

Here is my take...

1. Unless the slip yoke is particularly long the amount out of the trans is excessive.
2. There appears to be excessive play in your transmission mount
3. The video where you are raising the drive shaft up and down it looks like the U joint is moving.
4. The wabble in the drive shaft looks a bit much
5. I did not see any video of the rear u joint at the diff.

I would absolutely take the driveshaft to a shop and have them evaluate it. They will probably do it for free.

With the rear axel supporting the body weight, disconnect the rear u joint. Slide the drive shaft forward till it touches the transmission seal. Back it out 1 inch.


Measure from the center of the slip yoke to the center of the diff yoke.

See how that measurement compares to your driveshaft.

If it is more than 1/2 inch difference I would have a new drive shaft made.