Transfer case / trans fluid issues

Alright, 01’ vp24v , nv4500 , 4x4.
My transfer case fluid keeps on sneaking into my transmission! I fill my tc with atf till it runs out the fill hole. I fill my nv4500 with the Gm spec fluid ( that I assume based on price is squeezed from diamonds) . I drive 400 miles and the trans is overfilled ( and red) and the tc is almost empty. I pulled the tc and replaced the input shaft seal but it still does it. Any thoughts? Hopefully someone else delt with this before.

Is the vent tube clogged?

My old 2nd gen 4500 truck did this also.
I just filled the transfer case with the spec 4500 fluid, and it lived a happy life. Like over 100k miles.

Keep topping off the transfer case until they find their level.

I’ll check the vent, the shit that 2nd gen owners put up with is crazy, hahahaha

Sounds like a pressurized tcase to me. Clogged vent hopefully. I’ve almost never heard of t case fluids in trans. It’s usually the other way around.