Abstract: A method to prevent overspeed of an internal combustion and attached ancillary devices in a mechanized vehicle includes one or more procedures to prevent improper gear selection to disengage the lockup function of a torque converter, to initiate engine braking and to destroke variable displacement hydraulic pumps. Requested gear selection in downshift is allowed only after interrogation of brake pressure, ground speed, shift selection requested and torque converter output speed. The torque converter lock-up solenoid is activated or deactivated in response to torque converter output speed which is compared to selected values to engage or disengage. Engine braking using a compression release braking system response to engine RPM in manual or automatic mode to prevent overspeed. Variable displacement pumps are destroked in response to engine RPM by adjusting swashplate control.