My truck as 80k miles, and I don't know the maintenance history. I would like to change all the fluids in the differentials and transfer case. I have a few questions: Diffs: * My manual says that the front diff uses 80w-90 for "Four-Wheel Drive" models, and 75w-90 for "All Wheel drive" models. Since mine is electronically selectable (Auto, 2H, 4H, 4L), do I assume that's the Four-Wheel drive model? * What is the approx capacity of each diff? I can't find this listed anywhere, and I'm not sure how much fluid I'll need for each. Transfer case: * Again, Auto vs. Four-Wheel. For Four-Wheel drive, the listed fluid is AUTO-TRAK II. Is this available at any part store, or a GM only part? * My Haynes manual lists close to a dozen Transfer Case models. How do I identify mine? Is there a tag on the case? Thanks!