Replaced front differential and transfer case fluid today. Will do rear differential tomorrow or next weekend hopefully. Just passed 98,000 miles and the front differential and transfer case have never been changed, rear was changed by me at about 45,000 miles, so it's time for all three.
Fluid looked great in both and I'm sure they could keep going much further, but a lot of paste was on the magnet in the front differential. Breaker bar was needed to get all the fill and drain plugs off, especially the front differential drain plug. Holy hell that thing was practically welded on. Used Royal Purple Synchromax in the transfer case. It's listed as a substitute for the $55/qt. Toyota 75w fluid the transfer case calls for and is a lot less expensive. Needed a little over a quart.
I Used Redline synthetic 75w85 in the front differential and I used it in the rear differential back at 45,000 miles. I was able to fill the transfer case directly from the bottle with just a short length of tubing on the nozzle. For the front differential, you'll absolutely need a pump. There's no room to lift the bottle up. I don't know what the dealerships charge for these services, but my total cost for fluids and gaskets was right around $100, so you're almost certainly saving money, as I assume it's at least $100 per, and you're getting the correct fluids in each case rather than just 75w90 in everything.