The difference between the half-ton and the three-quarter-ton truck is payload capacity. A half-ton truck can haul roughly 1,000 pounds, while the three-quarter-ton truck can haul 1,500 pounds. This includes passengers, cargo and the tongue weight of any trailers it may pull.
The differences between half-ton and three-quarter-ton trucks are vast. The higher payload-rated truck usually has a heavier/stronger frame, an upgraded suspension and a more powerful driveline. Most three-quarter-ton trucks have a diesel option that comes with a further upgraded transmission, transfer case and axles. Most half-ton trucks are used for all non-commercial work short of being used as larger campers and horse trailers.