Ok, so I know that at 30k there is recommended maintenance which includes the changing of the tranny fluid and differential fluid.

First stupid questions: What is 'differential' fluid, what does it do, and why does it need to be changed?

Also, on my past vehicles I would have the tranny fluid changed every 20k to 30k. Never had a problem and every time the fluid would still be pink. However, I have read some posts on this board where changing that fluid could actually be bad..? I forget why.

Anyway, I would say that 85% of my driving is highway driving, mostly on cruise control. Can someone with my driving habits go longer between fluid changes or should I have them done per the maintenance schedule outlined in the owner's manual?

One more thing, how important is having the radiator flushed & filled? Is this something that should be done on a yearly basis or does it not really matter?

Let me try to answer some of your questions as best as I can:

differential fluid is the fluid inside your differentials. If you have a 4x4, you have two diffs. If you have a 4x2, just one diff, in the rear. It keeps your running gears (inside the diff) lubed up etc, so you need to keep it clean. In my experience, you can go along time between changes if you don't off-road into water etc...... To be safe/anal, I replace at every 30k miles or so... It's easy enough to do... If you do go into deep water etc, then obviously, you'd want to check the oil for water infiltration.

as far as changing tranny fluid, that's not a bad idea BUT flushing might be depending upon when the last flush was. If you have a brand new car, and flush every 30k, no problem. If you have a truck with 100k on it and it's never been flushed, you may loosen big crap up internally with a flush....potentially pluging line up etc...

i'd go with what the manula says, just to play it safe and clean....

the radiator doesn't need flushing every year, probably something like 3 years, but whatever the manual shows, I'd do....

hope that helps...

If I was driving that far everyday, I definately wouldn't be taking the X regularly. I'm only about ready to hit 20K on the '05.

Owner's manual should tell ya.