is there a brake-in period for new gears in the rear?

 

Yep...as many heat cycles as possible without getting on it. I did 5 heat cycles (minimum recommended is 4-5), and I've had mine in for over 2 years with more launches than I can remember and no increased whining.

 

what is a heat cycle?

 

Basically, go out drive normally for about 10 miles, then park the car for few hours so they can cool down. Then go out again and do the same thing for 10 miles, then let them cool.
do that like 2-3 times, then the gears should be fine to get on them hard.

After the heat cylces, most people usually change the rear end fluid, but you dont have too..