This is a common problem, as trueX5er pointed out. Bimmerfest has a larger X3 board and I've read many complaints from those with the 3.0si.
http://www.x3world.com/x3-e83-forum/...x3-owners.html
I've mentioned my reasoning on Bimmerfest, but basically BMW screwed up on both the programming and gearing. They dropped the 6-AT with shorter ratios into the X3 for '07 and paired it with an even shorter final drive than previous models. The result is gearing that is far too short, especially considering the N52 engine has more power than the M54 motors.
There have been a couple dealer service bulletins re: the auto gearbox programming. However, sad to say.....not all the reprograms stick, and results may vary. There is no guarenteed fix, except to purchase a manual X3. Indeed, it has gotten to the point where I am steering friends and forum members away from the '07 X3 6AT and recommending a manual gearbox, or else look elsewhere.