According to the Chrysler/Jeep, they use 75w-90 or thereabouts in regular open diffs and 135-140 (something like that) in the limited slip models. As far as 4wd, well, its an SUV without the U (2wd), so I didn't bother asking. I can't remember if the dealership used synthetic or not, but I'm sure they claim it needs it and therefore costs more.
So basically, that sounds right that they would use a thicker sludge in the LSD models.