[Pyrotechnic]

The "Heavy Half" and "Big 10" or "heavy duty chassis equipment" option for the most part is 3/4 ton springs with a 5 lug rear axle and 5 lug front rotors.

Parts of the package:
3/4 ton front springs
3/4 tons rear springs (several inches longer than 1/2T springs, shackle hanger location is further back on the frame)
Wider rear brake drums and shoes for better stopping ability
2 piece drive shaft for long beds
Double hump transmission crossmember for true dual exhaust (no cats)
Very minimal emissions equipment

A lot of the time, I think GM created these trucks as a loop hole. By upping the GVWR with the 3/4 ton springs, it bumped these trucks in the non emissions category the usual emissions garbage and catalytic converter don't have to be there. However, they really are better for hauling, towing, etc.