With light trucks the amount of weight in the bed of the truck makes a big difference in how the truck stops and how the brakes should be adjusted. When the bed is empty, the back end is very light and the rear brakes will lock up very easily. When the bed is loaded, the back end is heavy and the rear brakes will not lock up as easily.
Newer pickup trucks have a sensor that will adjust the amount of braking depending on the height of the bed, compared to the differential. This ensures good braking with or without a load in the back.
On my '59, the brakes are adjusted so the rear wheels will lock up with no load in the back, especially on wet pavement.
Remember brakes are probably #1 on the safety list.
