350Z Gearbox Slipping

Sounds rough. I had similar symptoms on my old BMW X3, although it was the automatic gearbox acting up there. Did you check the gear oil? Maybe there's mechanical wear in the transfer fluid?

Yeah, I've checked the oil level, and it seems fine, but I didn't check the oil condition. What did the mechanical wear in your case look like?

For me, it turned out to be defective gears in the gearbox. But it could be also gear wear in your transfer case. I'd take it to a workshop to get it checked out properly.

Thanks for the advice! Took it to a shop, and you were right. It was defective gears in the transfer case. Cost me 330€ to get sorted.