Limited Slip Read Diff on 2004

I just talked to the service department at a local dealer and they said there are 2 different diffs for the 2004. One has limited slip and the other does not. They said it is an option but I can not find this option in any of the material that Dodge has on their web sites or broshures. Is the limited slip diff part of another option like "tow Group" or "Heavy Duty Service Group"? Is it a custom "non advertised" option?

Shawn

I have a 2004 durango limited 4x4 with tow package. I have a 3.73 limited slip, which it comes with. I could have upgraded to the 3.92, but the dealer said it's a good upgrade if you will be towing very heavy.