Im sure this has been talked about but I cant seem to find a striate answer. I am have a 15000k service done tomorrow and want to change my gear box oil as I have heard that putting better grade oil in makes it smoother in the gear changes. Also should I change the diff oil too. I haven't done any mods yet but am planning to in the next 15000 I will only be chasing about 330rwkw. Thanks for your advice.