There are three ways to "Overload" a truck. Overload the axles, the gross, or the bridge weight. DOT doesn't care what the Army said their weight limit is on a particular truck. Loading the truck is always a compromise, under existing conditions that you have at the moment.
Conservative States use 34,000# per tandem group & 10,000# per single axle OR what the tire size is, ie., 550# per inch of tire. With each truck, some of the loading procedures come from "trial & error". How the truck handles the weight, generally depends on how its loaded, where, and tire pressure. TP is a compromise too. On these under-powered MV's TP is really important. If you have a Max load, you need Max TP, but the truck will handle like an over inflated basket ball, empty.
Like on a Deuce where you have a mid-point suspension between the rear axles, its real important to balance the load over that point, or just slightly ahead, or you might not have proper weight on the steering. If you have a max load, but not max TP, you can loose a whole gear on the highway - the truck won't pull it with soft tires & you'll have excessive wear on them.
Lee in Alaska