[valiant67]

If ATF+3 is recommended for a transmission, ATF+4 is even better, even in a 3 speed in a 1998 Voyager (which is a lockup).

Back in the day, drag racers would use Type F in their Torqueflites for firmer shifts.

I agree, it was a somewhat common trick. I had a RWD 904 transmission rebuilt years ago and the guy set it up for Type F fluid. I'm sure it was overkill for a car that was otherwise a dead stock 360-2.