A malfunctioning governor can be diagnosed by which of the following methods?

The method of diagnosing a malfunctioning governor is effectively accomplished through a road test or hydraulic pressure test. The governor plays a critical role in regulating transmission fluid pressure and modulating shifting based on vehicle speed and load conditions. A road test allows a technician to observe the transmission's shifting characteristics under various driving conditions, which can reveal irregular behavior indicative of a faulty governor. A hydraulic pressure test measures the actual fluid pressure in the system; deviations from manufacturer specifications can suggest governor issues, such as incorrect pressure regulation or failure to respond to engine load and speed.

While other methods might provide some information, they do not directly diagnose governor performance as comprehensively as these tests do. For instance, conducting a stall test in neutral evaluates different aspects of the transmission, primarily focusing on the torque converter's ability to stall, while unhooking a vacuum hose could potentially lead to a temporary change in behavior, but it’s not a standardized method for assessing the governor specifically. Therefore, performing a road test or hydraulic pressure test is the most effective and direct way to diagnose a malfunctioning governor.