Seems the newer fluids seem to cover what came before. Dex V is ok for Dex 3 and so on. At least that is what I've been led to beleive. Like I said, it's all voodoo to me....Other than swapping them out, I don't do autoboxes. The letters are important, but the Mobil1 (and I assume R.P.) seem to cover them all...I'm too lazy to walk out to the garage to read the label.