There were quite a few problems mostly with early production X5's. There have been numerous updates since then that have pretty much dealt with the problem. I have an April build 4.8 and the only issue is that it holds gears on hills which I don't mind.

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Porsche 996 Turbo (Ruf 550)
Porsche 993 Cab.
Porsche 997 GT3
Audi A8
BMW X5 4.8 White, Black Napa, Sport, Technology, Premium, Prem. Sound, Cold Weather, Rear Climate, Multi-Contour, Sirius, HD Radio, Running Bds., Bamboo