5w-30? Do you mean 90w-130? 5w-30 is not really a trans fluid, but I
would take that over nothing in a pinch.
Many new transmissions and transfer cases take ATF as the fluid, I think
it improves fuel economy and seems to work fine.
Most people don't think of ATF as being a suitable gear oil, but it has good
anti-wear properties and frees up HP too.
I mixed up a slippery batch of 1qt Lucas synth and 1 qt Mobil-1 synth ATF
for my t-case, I figured it to be as good as manual transmission fluid at a better price