My wagon with an N52 engine (3.0) did something similar. it would crank and run but upon slowing down it would stall and die on me. it turned out for me that the Crank Position Sensor was kaput. changed it and no stalling for me. worth checking out if you can pull codes from the car. I used MyCarly from my phone and reconfirmed using the INPA software.

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2002 325XiT 5sMT
2006 530XiT 6sAT