I have the same problem with mine but I have tried the above mentioned fixes and it does not really change the 3-4 shift. So what I do is hold it in 3rd and shift manually at the same time I back off on the throttle. I was told that I have very little time left with this tranny but I have also been told it could last forever(almost). What do ya all think?
PS. I just changed oil in trans too.
82 300SD 100k
91 Caprice SS
92 Jetta TD