Mercedes Benz ML Running Rough, Starting & Power Loss Problems

Fails to start after sitting all night. Once primed with easy start fires up no problem and will start all day long. Glow plugs and glow plug relay changed.

The fault message says “drive to nearest workshop without shifting gears” plus a message that the vehicle is not in park (but it would have to be otherwise I wouldn’t have got the key out of it) and another message about reset the run...

My ML320 starts up fine but after a few minutes it starts to run sluggish, when I stop the car is trying to go forward and I have to hold it with the footbrake. When I drive off again if I switch the ignition off and on it clears the fault....