1996 GMC Savana Van Owner's Manual - Page 224

Rocking your vehicle to get out: it NOTICE: Spinning your wheels destroy partsof your can vehicle as well as the tires.If you spin the wheels too fast while shifting your transmission back and forth, you can destroy your transmission. For information about using tire chains on your vehicle, see "Tire Chains" in the Index. First, turn your steering wheel left and right. That will clear the area around your front wheels. Then shift back and forth between REVERSE (R) and a forward gear, spinning the wheels as little as possible. Release the accelerator pedal while you shift, and press lightly on the accelerator pedal when the transmission is in gear. If that doesn't get you out after a few tries, you may need to be towed out. If you do need to be towed out, see "Towing Your Vehicle" in the Index. 5-36