Before or after, doesn't matter these days. Ford tells you to put it after the radiator, but the the instructions I've seen from the aftermarket coolers instruct you to install before the radiator. I personally prefer installing them before the radiator.
And I've read this opinion before on numerous occasions regarding making sure the tranny doesn't run too cold. IMO, this is foolish to be concerned with. I can assure you that there's a nary a first hand account to be found where someone's tranny failed due to being too cool.