A method of operating a vehicle powertrain system comprising an electric motor and transmission where the electric motor is operably and selectively coupled to the transmission and adapted to provide an output torque contribution thereto, and the electric motor has a predetermined maximum motor output torque and a predetermined minimum motor output torque which are used to determine a range of permissible control points for at least one transmission control parameter. The method includes establishing a motor torque reserve by performing at least one of decreasing the predetermined maximum motor output torque to a maximum reserved motor output torque and increasing the minimum motor output torque to a minimum reserved motor output torque, wherein the maximum reserved motor output torque and the minimum reserved motor output torque are used in place of the predetermined maximum motor output torque and the predetermined minimum motor output torque, respectively, to determine the range of permissible control points for the at least one transmission control parameter.