Vibrations and Stalling issues

[Titan]

Hi Guys

Had my X5 away on its first decent run last week and am concerend about two things that have manifested themselves so far.

Firstly, driving through constant speed sections of the motorway network produced a finger-tingling high frequency vibe through the steering wheel that could also be felt on the foot rest. I believe it is too high a frequency for wheel balance to be the culprit plus, shifitng the transmission into sport mode (ie higher revs at the same road speed) reduces the symptoms.
I have since noticed similar vibes in 30mph zones and when the engine is under increased load going uphill.

Secondly - it stalled in the middle of a (fortunately quiet) junction. There was a lack of throttle response, then the engine simply stopped. The car had been parked facing uphill overnight (it's normally on the level) and had travelled less than half a mile when it stalled. Ignition off/on  and it restarted first time but nonetheless very un-nerving!

It's booked in under AUC warranty at the dealers next week for diagnosis but I'd be interested to hear any thoughts on possible causes, cures and similar experiences.

Cheers!