Ford Mustang 2017 Owner's Manual page 114

Transmission
Note: Do not rock your vehicle for more
than a minute or damage to the
transmission and tires may occur, or the
engine may overheat.
If your vehicle gets stuck in mud or snow,
you may rock it out by shifting between
forward and reverse gears, stopping
between shifts in a steady pattern. Press
lightly on the accelerator in each gear.
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Mustang (CZG, CZY) Vehicles Built From: 02-05-2016, HR3J 19A321 AKA enGBR, First Printing