There is a Service bulletin (search) that was posted a while ago, where the X3 may hold 3rd or 4th gears too long on an uphill. I had the update done and it was noticeably better. A slight side effect was the gearbox tended to be a bit aggressive on the 5-4 downshift to maintain the speed, but my gearbox has adapted to my style and stopped doing that.
Now, my X3's gear logic is near flawless. Now if only our '06 325i would behave similarly............
