I ended up doing the rear differential last evening. I really wish there were separate drain/fill holes. Having to get a pump to drain and another pump to fill was a PITA.
I ended up going with Royal Purple 75w140. The stores near me were all out of Mobil 1 75w140, and I couldn't get a hold of the Amsoil reseller near me. And of course, after I bought the Royal Purple, I found it cheaper online with free shipping:
http://www.americanmuscle.com/royalp...0-gearoil.html
I just had to register my phantom Mustang