Mrathell,

If you have your original car book, read up to see if your transmission is "lifetime" or if it needs to be changed every 100,000 miles. Under the service pages, it will tell you what to do.

Many power steering fluids are changed by the dealer/BMW to use ATF. This is why they will write ATF on the power steering fluid reservoir cap.

I have a 2006 X5 4.4i. All 2006 X5 4.4i require a 100,000 mile automatic transmission fluid, seals and filter change per the BMW service pages. I did mine at about 103K miles, and am now at @ 112k miles, with no problems. Always use OEM ATF, seals, plugs, and filter change.
Like many here have said, If the OEM parts/fluids are good enough for BMW, they should be good enough for you to replace with. Don't play around with "as good as OEM", or "better or higher rated than OEM". parts, unless you know if it fails, it will only cost you that part, not an engine, transmission, etc.

Again, as for the transmission, check your book. I've read that some X5s came with the "lifetime fluids". Your book will tell you your specific case.
I've also read that BMW considers lifetime fluids to be 100k life!

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Douglas
2006 BMW X5 4.4i Sport