Fluid change time, synthetics??

I want to change the rear diff and T-case fluids. Anybody tried anything other than regular ATF in the transfer? I'm going to try and hunt down some synthetic gear oil for the diff., but the t-case has me wondering. B+M makes that "trick shift" ATF substitute, but I'm not building a fancy TH400 here.

Ideas?

I just put Mobil 1 ATF synthetic in my transfer case Saturday. Drives just the same , I'll really be able to tell in a few thousand miles when I change it out again. I just wanted to put it in there because of its higher resistivity to breakdown when heated, it can get hotter before it stops doing its job. The transfer case does warn up more when in 4WD compared to 2WD but I wouldn't say it gets hot enough to start breaking down non synthetic oil, I just like any added protection I can get.

Goodluck,
Synthetic all the way!!!!