So interested to see what's causing the shudder. I have the exact same problem.

 

Update.

Last weekend I removed the clutch/pressure plate combo. While the driveshaft was out, I inspected the u-joints. They were all fine.

The old clutch/PP seemed all right. See the pics attached. I was a bit discouraged but I decided to install a new disc and a new PP to eliminate another possibility. The old clutch disk has been regarnish before. Could the problem be related to this?

I started the car with the new clutch on the jack stands. I had the same vibration when releasing the clutch in a quick movement than with the old clutch.

Then I decided to do a real test drive. I drove the car for 30 mins. I stopped the car in a slope and tried to get the car moving a few times. No vibration at all. What a great feeling after more than one year of searching!!

I'm not 100% sure everything is fine as I didn't drive the car enough. Will see when the weather here gets better but it is for sure an improvement.

As jfantis mentionned the vibration on the jack stands may be normal when no load.

On a side note, when having the right tools the clutch/pp job isn't too bad.

 

Glad you got it sorted!
Your pp looks way better than mine did, so maybe that was the cause of my issue, too.
Either way, congrats!

 

So a new clutch work for you?
I have the same vibrations on take off

 

Yep.

So far so good. But I have not done a lot of mileage since the clutch replacement.

 

If you also have the flywheel checked and it turns out true that may be the end of it. Could have also been out of adjustment, bad bearing etc.
Tough to say. Sometimes just changing parts without pinpointing it can solve it if you get lucky. May be the case here. Good luck.

Sounded like clutch to me

 

Any drivetrain vibration I've ever experienced is PPF or diff bushings. Also cracked my PPF and it was hard to spot. Welded it all up and installed new dif bushings and did brace. Are all yor trans tunnel braces there? Also how are your motor mounts?