most dont.
the way i understand it is it needs to unlock for certain shifts to not break internals, so to keep from locking/unlocking all the time, its alot easier on things to just leave it unlocked.
life of the tc will go up.
as i understand it. could have misinterpreted the explanation though.
I aint an auto tranny guy, but also isn't the 2 to 3 and 3 to 5 shift complicated...its not just synching in those shifts? I can't remember the details though.