The "ton" rating is nominally what you could tote on the back of the truck. However it is no longer an accurate number and has become just a guide to general size of truck. The actual payload capacity is reduced by the bed weight, a considerable variable.
11,000 lb gross vehicle weight is total of everything, truck, bed, fuel, driver, load and everything as it rolls down the road. 11,000 lb less all that only leaves room for only a few thousand pounds of payload, something like your nominal "ton and a half" rating.
