"Light Load" button on 08 Dash?

Buddy of mine picked up SUPER clean 08 2500 6.7L 6spd last week with only 68K miles.

We looked through the owners manual but cannot find anything explaning what this button does? Its to the right of the exhaust brake button.

That is for the air pressure sensors in the wheels, if you press that you can run reduced pressure in the rear tires (45 psi I think) for a better ride when not running loaded.

The Tire Pressure Monitor System (TPMS) “LIGHT LOAD” reset switch will allow the driver
to switch between the MAX LOAD INFLATION PRESSURE (COLD) low pressure warning
threshold and the LIGHT LOAD INFLATION PRESSURE (COLD) low pressure warning
threshold depending on the vehicle's load condition. The tire and loading information label
defines the recommended front and rear cold tire inflation pressures for the vehicle when
operating in the MAX Load condition. A SUPPLEMENTAL TIRE PRESSURE
INFORMATION label is also included defining Light Load tire inflation pressures when
operating in the Light Load condition. When the “LIGHT LOAD” reset switch LED is ON,
the TPMS is using the light load inflation pressure (cold) low inflation warning threshold.

Thanks guys!