The greatest damage to any new ring & pinion gearset usually occurs during the first hundred miles. During this time, the new gears are bedding-in which generates quite a bit of heat and if driven hard you will raise this temperature even further and may cause irreversible damage to the gears. This is because the gears need some run-time to allow the machine surface finish to wear itself to its final match. The ring & pinion gears are now lapped in but they still must have sufficient run-time to allow the surface finish to properly develop. 

Over the course of a few  thousand miles the gears will bed-in, increasing the load bearing surface area while polishing themselves up nicely to where they are smooth and shiny.  This improved MSF (machine surface finish) reduces the heat that is generated and the larger load bearing contact area increases the overall durability of the gearset. It is wise to let the transfer case ring & pinion gears bed-in before pushing them to their material limits.

Recommend procedure for breaking-in your ring & pinion:

Follow the rear differential filling instructions provide on the FAQ section of this site. It would be best to keep vehicle speeds should stay below 60 mph for the first 100 miles. Drive the vehicle 10-20 miles, stop and let cool for 30 minutes.  Repeat this process a few times before driving the vehicle at highway speeds. Do not abuse or dump the clutch or do any hard acceleration, let the ring & pinion bed-in gently. If you take it easy on a new ring & pinion and perform regular oil changes it will last much longer.  Use caution when letting out the clutch, as aggressive high rpm clutch dumps can fatigue parts and may lead to eventual failures.

New or recently rebuilt rear differentials should have the oil changed somewhere between 500 to 1000 miles and again after 5000 miles.  TRE adds a Moly assembly additive, do not be alarmed by the color of the oil when you first change it.  Vehicles that are being road raced require race car maintenance and all drivetrain oils should be inspected after each race and changed if the oil is dark or stinky. Road racing applications may add an additional pint of oil to the rear diff for added lubrication and cooling.

Rear differential oil recommendations