I changed these fluids/oils as preventive maint starting from the 15k mile svc.
Yeah the dealer service rep looked at me all crazy - but its my car and I have my boyfriend's experience to guide me on the fact that there is NO SUCH THING
as a lifetime fluid. For most systems it is the very first fluid change that is most important in the overall life if a car.
Power steering (15k miles)
ATF (15k miles)
Center differential (36k miles)
Rear differential (36k miles)
Coolant (36k miles)
Brake fluid (36k miles DIY with BBK it was getting bad too at this mileage)
Oil (Royal Purple + Quaker State synthetic every 5-7k miles mostly every start of winter and early summer)
No two situations are alike.
Hope this helps anyone to figure out your best maint intervals.