Abstract: A microprocessor controlling a shuttle shift transmission may be programmed while the gearshift lever is in neutral to preselect a forward and reverse gear into which the transmission is shifted when the gearshift lever is moved to a forward or reverse position. The microprocessor may also be programmed so that, in shifting between forward and reverse, the forward and reverse gears selected differ by a preprogrammed amount. The microprocessor may be programmed to control vehicle deceleration by selecting gears in the transmission so that the transmission and/or the vehicle engine become a load for decelerating the vehicle. In a diagnostic mode, the microprocessor executes a routine to develop a clutch calibration value which may later be used to insure uniformity of clutch operation in different vehicles, or in the same vehicle over a period of time. The normal speed ratio matching which normally takes place when shifting gears may be manually overridden by operator manipulation of the gearshift lever.