A post from 3 years ago:

Quote Originally Posted by Manxmann View Post
Isn't the autobox the 4r70w? If so you must use Mercon V, Dextron III is not a substitute for Mercon V but _IS_ for Mercon, using it will cause your box to fail.

I have a 4r70w in my New Edge Mustang and went through this pain. Interestingly my stang is supercharged and the 4r70w holds up like a champ many owners saying they are stronger than the manuals. Did I read on here that the R75 couldn't be charged due to gearbox weakness?