just run it until it blows. I don't like mine because it shifts sloppily and hard, and when it's cold it doesn't act right until I've been running it for awhile. You could always look into other auto
trans. that ford used in later years. I've never looked into it myself and the mustang didn't change that much so there might be a better model that you could shoehorn in, if you're that dissatisfied. I don't like the
trans in my car but switching to a manual would be a bit of work, and if I'm going to do that I'd be just as far ahead to upgrade the motor.
Personally I'm going to keep mine until it blows and then decide if I'm junking the car or ripping out the driveline and putting in something clearly superior. After all, there are not many cars cheaply available today with strong aftermarket support and enough room under the hood to allow for pretty much any motor you want, any transmission you want, etc. It goes back to the old question : "Speed costs money, how fast do you want to go?"