These two elements work together to determine shift points.
Let's look at it this way.
The
governor is just a road speed indicator, telling the transmission only how fast you are traveling. It generates a pressure curve, starting at 0 psi, that rises as you accelerate.
The shift valves in the valve body are held closed with shift-valve springs. The governor pressure works against the opposite end of the shift valve train, and strokes the shift valve when the force is sufficient to overcome the spring force. Problem with my simplified model is, it wants to upshift at the same road speed regardless of driving conditions. Enter the modulator.
The
modulator is the transmission's load sensor. As the engine vacuum signal diminishes modulator pressure rises. This pressure is sent to the main pressure regulating system where it boosts line pressure to meet increasing torque demand (i.e. clamping force on the clutches). Modulator pressure is also distributed to the shift valves where it works against governor pressure in trying to keep the valves in the down-shifted position. That is why your shifts get later & more spread out as you stand on the load pedal.
That being said, once you are at WOT, the modulator signal is static; atmospheric. Now the governor characteristics are going to be the determining factor as to when the shift occurs.
When adjusting WOT shift points, you usually want to make changes to the smaller, secondary weights and springs. It's a centrifugal device so lighter weights & weaker springs translate into higher shift points.
Class dismissed. 
