OK, most of the time when I see a 4.6 equipped Ford, like my 01 F150, it has a 4R70W trans. They come in lots of cars, and are good for light duty stuff. I see a lot of 5.4 equipped vehicles with a 4R100 trans, more heavy duty. I bet the rating is just to cover Fords rear when you fry a 4R70W. Also not all 4R70's are built the same, some come with more clutches or other upgrades, or an enhanced shift pattern programmed into it.

The 4R70W likes to run HOT, I put an aftermarket cooler in line AFTER the stock cooler on mine. The cooler you can keep these things, the longer they will last you. Allways use Merc V fluid in it and you should be fine.