Thanks for the responses; the factory tires are g rated so a little over 4k each.
With a 3150 pin weight that leaves roughly 17k on the suspension components; spings and hangers etc. a two axle in the same model line has GvWR of 16500 pretty close to 7k an axle plus pin weight for the model... provided all things are equal just trying to figure out “why” the third axle only nets 3500lbs of added capacity to the trailer. Wondered if if it’s merely a regulatory thing? Have to classify differently over 20k? Meet other restrictions over 20k? Or if it’s actually a physical capability issue?