What is making my auto transmission shift harshly on my 1998 Mercury Sable? I changed its fluid but it didn’t help.
One of the common reasons is that its basically about used up.
But there can be lots of reasons. It could be as simple as a bad mount. What you want to do is ask around among people that you know for your best local-area independent transmission shop. Take it to them for an evaluation. If you get one post all of the info you have including whether it was scanned for errors and, if so, what the error codes were.
The other kind of info people need is basic stuff like mileage on the transmission and its service history.