Motor Selection help required

I need a motor with peak torque of 50 Nm , 1 to 5 rpm.
Very High torque, Very low RPM.
Torque to be controlled on command. From 5 Nm to 50 Nm.'
In steps of 5 Nm.

Please revert with the specs of motor and PLC

It will thus be a gear-motor. Torque for a DC motor is dependent on current, so you'll need a motor controller with current-control.

That torque and speed imply about 25W ignoring gear losses, so perhaps more like 50W.