A method of propelling a mobile work vehicle having a hydraulic circuit system including a propel circuit and a work circuit powered by a hydraulic pump structure, the propel circuit including a hydraulic accumulator and a hydraulic propulsion pump/motor for powering propulsion elements of the work vehicle through a drivetrain, the mobile work vehicle also having a transmission mode supervisory control state machine having a hybrid propulsion mode (84a, 660) and a hydrostatic propulsion mode in which the hydraulic system undertakes tasks that result in high pressures in a high pressure line without exposing the hydraulic accumulator to the high pressures, the hybrid mode (84a, 660) allowing the exchange of energy between the hydraulic pump structure, the hydraulic accumulator, and the pump/motor, the method comprising: determining if a current propulsion mode is the hybrid propulsion mode; determining if a selected propulsion mode is the hydrostatic propulsion mode; characterized in that the transmission mode supervisory control state machine also has a first transition mode and a second transition mode and the method also comprises: entering the first transition mode from the hybrid propulsion mode if the selected propulsion mode is the hydrostatic propulsion mode and the current propulsion mode is the hybrid propulsion mode, the first transition mode controlling transitional behavior when switching from the hybrid propulsion mode to the hydrostatic propulsion mode; setting an engine-pump displacement target when in the first transition mode; substantially matching the engine-pump displacement target to a system flow consumption when in the first transition mode; and closing an accumulator isolation valve when an engine-pump flow output matches the system flow consumption when in the first transition mode. determining if a current propulsion mode is the hybrid propulsion mode; determining if a selected propulsion mode is the hydrostatic propulsion mode; characterized in that the transmission mode supervisory control state machine also has a first transition mode and a second transition mode and the method also comprises: entering the first transition mode from the hybrid propulsion mode if the selected propulsion mode is the hydrostatic propulsion mode and the current propulsion mode is the hybrid propulsion mode, the first transition mode controlling transitional behavior when switching from the hybrid propulsion mode to the hydrostatic propulsion mode; setting an engine-pump displacement target when in the first transition mode; substantially matching the engine-pump displacement target to a system flow consumption when in the first transition mode; and closing an accumulator isolation valve when an engine-pump flow output matches the system flow consumption when in the first transition mode. entering the first transition mode from the hybrid propulsion mode if the selected propulsion mode is the hydrostatic propulsion mode and the current propulsion mode is the hybrid propulsion mode, the first transition mode controlling transitional behavior when switching from the hybrid propulsion mode to the hydrostatic propulsion mode; setting an engine-pump displacement target when in the first transition mode; substantially matching the engine-pump displacement target to a system flow consumption when in the first transition mode; and closing an accumulator isolation valve when an engine-pump flow output matches the system flow consumption when in the first transition mode.