Did you ever consider that the shudder may not be the transmission at all?
There are allot of thing that can cause a shudder... out of balance tire , bent rim, separated tire, drive line out of balance/bent, warped brake rotor, broken flex plate, etc.
Check everything.. a lot of mechanics anymore are not capable of diagnosing a problem if the computer diagnostics doesn't tell them what to change/look for... anymore they are just "parts replacers"
Always remember to check the simple things off the list first ...
