GMC 1993 Suburban Owner's Manual page 86

K231
If you have a manual transmission, you have a SHIFT light. This light will
show you when to shift to the next higher gear for best fuel economy.
When this light comes on, you can shift to the next higher gear if weather,
road and traffic conditions let you. For the best fuel economy, accelerate
slowly and shift when the light comes on.
While you accelerate, it is normal for the light
to go on and off if you quickly
change the position of the accelerator. Ignore the SHIFT light when you
downshift.
Four-wheel Drive Vehicles Only: I f
your vehicle has four-wheel drive and is
equipped with a manual transmission, disregard the shift light when the
transfer case is in
4
LOW.
ocking
If you have this feature, your rear axle can give you additional traction on
snow, mud ice, sand or gravel. It works like a standard axle most of the
time, but when one of the rear wheels has no traction and the other one
does, the locking feature will allow the wheel with traction
to move the
vehicle.
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