While driving at a maintained speed it will shut down then die. on 1998 Mercedes-Benz ML320

As I'm driving, mainly at higher speeds, 40 - 70 mph, the car loses all power. The tach drops to 5 then it dies. It's like there is a shut off swithch. I'm not sure if it is doing this when it tries to go into overdrive or if it is already in overdrive when it does this. It will start back up when I can get pulled over put it in park and remove the key and put it back in.

Asked by for the 1998 Mercedes-Benz ML320