First Oil Change

[06DurALLY21]

Just got a 06 HD with the duramax/allison, and already thinking about the first oil change. Just curious what brand everyone recommends for the first change? I eventually want to go to a synthetic, but figure I will wait till about 10k for that. Also is it true you have to change the rear diff fluid at 500? I read that somewhere, but maybe it was just if you tow with it. Thanks a lot John

[ZZ327]

mobil delvac, or Ive used Shell Rotella T in diesels