my friend suggested i get a Auburn HP Series Limit Slip Differential, what exactly does this do? and is it worth the money?

 

The 4.0 came with a 7.5" rear end and open differential. This will get power to both rear wheels - if you can find one to fit the 7.5" rear end.

It is more cost effective after the purchase and installation costs are factored in to just get a take off 8.8 from a GT or 2011+ Mustang and swap rear ends.