Dan wrote:

The rating of the brakes also plays in to the GVW.

Yes, but for a pickup in particular, the braking gets better with more
weight due to the much improved rear wheel traction.

Not true at all.

Yes, it is true, and it has been proven numerous times in actual
testing. Empty pickups have terrible weight distribution and the
addition of cargo in the rear greatly improves the weight distribution
and braking traction available from the rear wheels. Pretty much every
test ever done on pickup truck braking has shown shorter stopping
distances when significant cargo was placed in the bed.