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In addition to the very distinct possibility of a sticky 1-2 command valve, there is a similarly distinct possibility of a sticky governor. For a given road speed, the transmission output shaft speed, and hence the governor speed, is quite low due to the 2.24:1 final drive ratio. The internal 1st gear ratio is short (~3.7:1), and so engine speed is high for a low output shaft speed. If the governor is sticking from a stop, and then "pops" free, any subsequent shift behavior will be normal.