My gf's has a 93 Max, and the trans. shift very late (like at 4000 rpm even with very light throttle) so her dad changed the trans. fluid but nothing changed.

So today he got this "SLICK 50" High Mileage Auto. Trans. Treatment thing and put that in. The car drove fine for about 20 miles and then it doesn't want to change gear anymore. It doesn't shift out of neutral after the car comes to a stop, only shift to first gear after she turned the car off then start again, even then it doesn't shift to second.

So I guess the SLICK50 is to blamed? Does it help to flush the tranny and fill up with fresh fluid? Or we need to get a new tranny?