Hyundai Repair: 1994 Sonota V6 GL Automatic transmission, frequent failures, air breather

Question
My transmission is shifting really hard.  Research says that it might have a faulty Air-exhaust plug.   What is this and can I fix it without replacing the transmission?

Answer
A faulty breather would be a dubious reason for hard shifting.  I suppose it's possible, but I've never heard of it occurring.

I've never had occasion to even look for the air breather, but in most cases it's simply a pipe on top of the transmission with a cover loosely crimped onto it to keep dirt from getting inside the transmission.  

Your first steps, if you haven't done them, should be to check to make sure the fluid is in good condition and at the proper level, and then to have the car checked for transmission diagnostic trouble codes by a shop with tooling capable of communicating with the TCM.  

The chances of having a simple problem with this transmission aren't very good.  The most frequent failures required rebuilding or replacing the transmission.