I searched the archives on friday and found very little on this, as far as capacitys, some misinformation, and some differences from what was posted. My truck is a 2002 Z71 1500 4X4. I did both axles yesterday and here are some numbers and info. The front takes almost 3 qts of SAE non-synthetic 80W90. You need to pop off the front skidplate of a Z71 truck to allow the fluid to drain. 4 bolts. You could do it without removing the plate, but it could make a big mess. The fill/drain plugs are accesible with the skidplate in place. The lower drain plug is magnetic on the front diff. The rear differential takes just shy of 3 qts of SAE Synthetic 75W90. One thing that I was surprised to see(after I had purchased a cover gasket already) was that there is actually a drain plug on the very bottom of the differential. It is the same type of square head as the fill plug that you simply use a 3/8" drive extension directly to remove. The drain plug is a taped seat countersunk into the housing flush. I was prepared from reading the archives to remove the differential cover to drain the fluid. Not necessary in this case with a drain plug provided. GM does not recommend changing the fluids at any point up to 150K as specified in the maintenance, but I would recommend if anyone's truck is at or approaching 100K to do it anyway. My fluids were pretty black when drained at 140K. I also felt that since GM doesn't require the fluids to be changed, the OEM fluid must be pretty good, so rather than buy a decent Amalie/Kendall or Mobil 1 to put back in, I would rather spend the extra bucks and buy the fluid directly from GM. The rear sythetic is about $20/qt and the front is cheaper at around $5/qt. The gasket was $5 but I didn't use or need it as mentioned. The GM p/n's are in the owners manual for the fluids. Hope this info helps someone out when the time comes to do it.