You can go through this one. I asked the same question. Doesn't seem like there is an exact science on it.
http://www.camaro5.com/forums/showthread.php?t=206356
I'm about to have some 3.91 LPE gears installed next week (I hope) at ADM performance. Andy said at least 3 or 4 heat cycles before really getting on it. That's getting the rear heated up with probably 15 - 20 min of driving and then letting it cool down. After about 500 miles I'll change the rear end oil again.
I'm basically going to take it easy with just normal driving for a good week or so. I'm going to vary from just driving around at street speeds plus get it up on the highway. I'll probably do this after work mostly letting it sit over night to cool down.
Like you mentioned these are basically like the stock gears. Made by the same company. It wasn't long after I got my car that I was putting the hammer on it and my stock gears have never been an issue.....even with cradle and rear end bushings.
I'm starting to chomp at the bit for my gears. I've been waiting a couple weeks already. I think it will make a nice mod along with what I already have.