I recently flushed all fluids on my 4.8is as you are talking about doing, mine has 140k miles and probably never even had an oil change until I got it (seriously neglected 4.8is, I paid $5k for it as a project car). The only thing I couldn't get done was the front differential. How to people get access to that drain bolt?

Anyway, I opened up the transfer case to change out the fluid and nothing came out! Bone dry... GT1 was showing a code for transfer case "oil wear" but I wasn't expecting it to have no oil. Anyway, I filled it with .9L of the new stuff and don't see any kind of leak.. Not sure exactly what happened there.

I did one tranny flush and am about to do another one (tomorrow), I just wanted to get a good 300 miles in between flushes. The car drives WAY better after one, and I'm hoping it'll improve more after the 2nd. I still have a faint whine at low speeds. What could be causing this? Is it the tranny or the transfer case?