E39 540i Stalling at Highway Speeds!

Lately my 540i Six Speed has been stalling both at idle and while in top
gear on the highway! I manage to restart but it runs very rough then
smooths out but will eventuall need a restart soon thereafter. Sounds like
it's got Microsoft Windows inside!

Dealer said check engine code reveals a Cam Shaft Sensor code?? They told
me to change the plugs and fuel filter which I did but that did not help

Any ideas?

Thanks,

Brian