So the service dept looked at the car today and it starts and runs fine. They will keep and drive it another day, but now I'm quite concerned about driving around a car and having it die on me.
If anyone has had this problem or knows what it might be, please share!
One thing - I don't think the gas mileage is as good as it was - for city driving anyway.

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'07 X5, 4.8, Premium, Techology, Sport, & Rear Climate Pkgs, Black Sapphire, 3rd seat, Tobacco Napa w Bamboo.