Tonnage is a name, not a reality. My 1974 Ford 1 ton dual wheeled truck crossed the scales at 13,460 pounds. The tare weight was 7,230. That means my '1 ton' carried 3 tons and 230 pounds additional, or 6230 pounds. Of course back then they made TRUCKS. Not like todays things,a rule of thumb, if the springs will still react to your weight applied to the load, its not yet at capasity. If you can make the truck bed bounce it is not over loaded.
Of course that truck had a second set of springs, a 351 Cleveland engine, a 4 barrel Holly double pumper 750, a 4 speed New Processes, with a Dana 70 4:11 rear. And got 17 MPG!! Once pulled a 78,000 pound semi loaded with logs to a fuel station.