Had an autobox problem with my previous E46 330d. There was apparently a batch of 2002/2003 models that had GM manufactured trannies that didn't last...... ? After that ZF gearboxes were used and this alleviated the problem somewhat.
Never had a moments problem with my X5 3.0d except for an annoying and intermittent "check oil level" false warning since the last service.
Other than that I still feel amazed when I drive it. It always feels like I am driving someone else's car!! I can't believe I own it

Love my X5