ELSD only comes with quadra-drive, does your EVIC display Quadra-Drive when you push the start button? Does the rear diff have an electric motor hanging off it similar to the one hanging off the transfer case? You should see AWBP and DSFP on the build sheet for ELSD.
The 36,000 mile fluid change is for severe use. If you routinely take the Jeep off road through mud and water or tow heavy a lot, then change it, otherwise just check the level.
Current: 2011 Grand Cherokee Overland V8, 2009 Liberty Rocky Mt V6
Previous: 2000 Grand Cherokee Laredo I6, 1979 CJ7 I6 Quadratrac