I have a 2005 cummins with a limited slip rear end. I used to have. 99 1 ton cummins that was posi. My best friend has a 04 that's posi...did Dodge come out with a limited slip in their diesel rigs or do I have something weird going on???

 

Nope, you have a limited slip rear end. Its a TQ bias LS so it does not work like the 2nd gens that have clutches. You need power input for it to work, if you have an LS.

Your friend with the 04 doesn't have a posi unless it was added after the fact. All the 3rd gens had the same LS from the factory.