How can you tell the difference from a limited slip and an open differential?

Three ways:

1. Call a Dodge dealer with the VIN # and ask
2. There is a tag usually on one of the rear diff cover bolts that says what it is, ratio and what oil additive to use.
3. Jack up the back wheels and try turning one of the wheels. With the trans in park or for a manual in gear, in the limited slip the rear wheel will not turn by hand. The open differential will.

Except my truck, It has so many miles on that the guts inside the limited slip are so worn that it acts like an open diff for this test