Abstract: A method for shifting a powershift transmission of a vehicle in accordance with the load being experienced by the engine as estimated from certain engine operating parameters. A turbocharger associated with an engine operating at a given engine speed generates a turbo boost pressure. The turbo boost pressure is monitored by a sensor and a turbo boost signal is generated therefrom. Similarly, the engine speed is monitored by a sensor and an engine speed signal is generated therefrom. The turbo boost and engine speed signals are used to estimate the engine load based on empirical data stored in the transmission controller's memory, and a percentage load is computed therefrom. The percentage load is then used to generate an appropriate duty cycle and time value for a pulse-width-modulated shift signal which controls the modulation of an on-coming directional clutch into engagement at a desired rate of engagement dependent upon the load being experienced by the vehicle.