Toyota 2014 Sienna Manual page 240

2-1. Driving procedures
Changing shift ranges in S mode
When the shift lever is in the S position, the shift lever can be oper-
ated as follows:
The initial shift range in S mode is set automatically to 5 or 4 accord-
ing to vehicle speed. However, the initial shift range may be set to 3 if
the AI-SHIFT has operated while the shift lever was in the D position.
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Upshifting
Downshifting