Chevrolet 2004 Silverado 1500 Pickup Owner's Manual page 356

In order to calculate the amount of weight any front
accessory, such as a snow plow, is adding to the front
axle, use the following formula:
(W x (A + W.B.)) /W.B.= Weight the accessory is adding
to the front axle.
4-66
Where:
W = Weight of added accessory
A = Distance that the accessory is in front of the
front axle
W.B. = Vehicle Wheelbase
For example, adding a 700 lb. (318 kg) snow plow
actually adds more than 700 lb. (318 kg) to the front
axle. Using the formula, if the snow plow is 4 ft. (122 cm)
in front of the front axle and the wheel base is 10 ft.
(305 cm), then:
W = 700 lb. (318 kg)
A = 4 ft. (122 cm)
W.B. = 10 ft. (305 cm)
(W x (A + W.B.))/W.B. = (700 x (4 + 10))/10 = 980 lb.
(445 kg)
So, if your truck's front axle reserve capacity is more
than 980 lb. (445 kg), you could add the snow plow
without exceeding the front GAWR.