Did it already come broken in from Strange so that you get proper gear wear? From what I've been told a good way to break in a rear end is to put the car on jack stands, let it run for 15 minutes, then drive around on the streets for 20 minutes (nothing crazy), park it for 2 hours to let it cool, then take it out another 20 minutes. You may want to repeat that last step one more time before you take it out onto the freeway.