For example the f150 is rated for 1.2 tons, the 250 1.3 to 1.8 depending on configuration. gotta go to f350 for an 8 ton configuration.
For people who don't think about this often, imagine four 200lb guys riding in the cab of the f150. It's already a third of it's payload capacity at that point. Can't fit too many bags of cement in after that.
Of course this is moot in comparison to a minivan which has a payload capacity of about 3/4 ton. You’ll be over capacity in the minivan if you have a 175lb person on each seat.