DTS recommended using 85-140 non synthetic gear oil for break in.
Drive the car 30 miles and then let the rear completely cool down. Do this cycle 3 times. Then after 500 miles change the break in oil to lube of your desire. They recommend Amsoil 75-90 full synthetic.

This is the procedure for a car that will see some street duty.

This comes from company that has built thousands of custom rear ends.