Chevrolet calls for replacement of transmission fluid, transfer case fluid at 50,000 miles. They say coolant should be flushed at 150,000 miles. Differential fluid is not listed, but I would recommend it be done at the same time as the transfer case as a proactive measure.
Keep in mind I am referring to a "Severe Duty" schedule, because most of America (metro America anyway) deals with idling time and load carrying which defines severe duty requirements. Besides, the more maintenance, the more proactive you are being, the better prevention you are providing.