It's a 1/2 ton truck made to compete with the chevy 1500, ford F150, and ram 1500. Toyota doesn't make a 3/4 ton or 1 ton model, they decided to not compete in that market.
The big three's heavy duty pickups (3/4 ton and 1 tons) have certain attributes that the 1/2 tons don't have like heavier frames, bigger brakes, heavier suspensions, full floating axles, heavier transmissions, etc. It's not really about engine horsepower since often a 1/2 ton will have more horsepower than the more commercially oriented 3/4 or 1 tons.
The toyota tundra is a great pickup, the best 1/2 ton made in my opinion, but it's still a 1/2 ton and not built to be used like a 3/4 or 1 ton.
