.9" is right for 2004 at least.

My local ford counter man -- pretty large and sucesful place -- says that the 75w140 synth is now standard and superceeds the older heavy diff fluids, regardless what your old manual or shop manual says. He has a ford counter manual that shows that.

So you can run the 75w140 up front too...

Ditto all the comments about needing LSD additive. I have a leaky rear. I've decided to mix up a quart of lube with additive so I can top it off (.9" below) whenever I need to.

And BTW, I too find it just plain stupid for Ford to design a diff case, where you have to use a wire bent like an "L" to find the fluid level. Like -- whatever happend to the good ole days where you filled to level of the filler hole and then you knew you had the right ammount in there......