Governor Oil Pressure and Modulator Oil Pressure are used to control your upshifts. Strictly Governor Pressure is used to control downshifts. For a forced 3-2 downshift, there is an electric solenoid activated by a switch located either on your accelerator pedal, or it could even be on the carburetor. Since this circuit is only used to control a downshift under heavy load, I don't know if this is a primary area of concern. If the weights on the governor are sticking, it could raise the line pressure and force it to shift earlier regardless of engine vacuum (modulator pressure). Is is possible that the 2-3 shift valve is sticking?