YYC-Sierra, thank you for the write up. I was going to take my truck to the stealership but after seeing this, I picked up AC Delco 75/90, 75/85 and AC Delco full synthetic trans fluid and did the rear diff and transfer case myself tonight. Doing the front diff tomorrow.
This was the first service at 52K and to be honest, the transfer case fluid was still red, the rear gear lube was dark but not a whole lot of metal on the magnets. I feel better now that it's done. I would have done the front diff tonight but I have a skidplate that needs to be removed, didn't feel like doing it in the dark.