Chevrolet Silverado Classic 2007 Owner's Manual page 577

If you have added a snow plow to the front of
your vehicle, lower the snow plow fully
before raising the vehicle.
CAUTION:
{
Getting under a vehicle when it is jacked
up is dangerous. If the vehicle slips off
the jack you could be badly injured or
killed. Never get under a vehicle when it is
supported only by a jack.
CAUTION:
{
Raising your vehicle with the jack
improperly positioned can damage the
vehicle and even make the vehicle fall. To
help avoid personal injury and vehicle
damage, be sure to fit the jack lift head into
the proper location before raising the
vehicle.
Front Position - All Other Models
577