A system for controlling the selection of the operative ratio of a vehicle powershift transmission driven from an engine via a main clutch. The system includes a clutch status sensor for sensing engaged and disengaged conditions of the main clutch. A selector is provided for selecting the operative ratio of the transmission. Also, a control circuit is provided which includes a ratio-change modulating function which, when the main clutch is engaged and a change to a non-adjacent ratio is selected, invokes a serial routine which ensures that each intermediate ratio between the current ratio and the selected ratio is engaged for a moment to ensure a smooth substantially jerk-free progression between the current ratio and the selected ratio. When the main clutch is disengaged and a change to a non-adjacent ratio is selected, the control circuit invokes a direct routine which permits changes from a current ratio to a non-adjacent selected ratio without engagement of any intermediate ratio.