Its synthetic gear lube.
For 2014 models, every 20,000 miles, inspect the front and rear axle fluid, change if using your vehicle for police, taxi, fleet, off-road or frequent trailer towing. Inspect means to check for leaks. Towing heavy creates a lot of heat that could break down the fluid early, off road there is a chance of water or dust contamination. Otherwise there is no change interval suggested.
Transfer case fluid should be changed at 120,000 miles.
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac