Payload refers to the amount of cargo weight a vehicle can safely carry.
For example: An over the road semi can gross a max weight of 80,000 lbs.
This is max weight including the truck, the trailer, the fuel and the driver. The payload capacity refers to the actual weight of the cargo which could be less than half of the vehicles gross weight. There may be room for more cargo in the trailer, but this would cause an overweight situation that could be unsafe.
The same is true with the Tacoma. Payload is the amount the
vehicle can safely carry. Overloading can change how the vehicle
drives in terms of steering and braking.