Strangely there was never any bottoming-out or grinding, the suspension didn’t make any audible noises, and I watched the tire pressure, I don’t recall exactly but it didn’t go up that much...
Well that's the thing, it probably never moved up or down, as it was likely on the bumpstops completely! 3,800lbs?
The truth is the suspension begins the sag process way way way before that, and getting every pound of payload in the bed of the truck (not dispersed) is kind of a toughy.
See Chevrolet is tacitly explaining that to truck owners with their new door sticker system.
Notice the max payload and the max tongue weight (on the trailer hitch) are different.
At around 950 on the hitch, that truck is sagged into position. It's essentially saying, you may have 1635lbs of payload on the truck, but the suspension would appreciate not every pound of it in the bed or on the hitch. THAT capacity number could be closer to 900 - 1,200lbs. (Again the factory rake is built in by design to let the user know, at the point "hey that doesn't look right.." when the truck is pointing skyward, to back off the loading) .
The remaining payload capacity to ideally be spread out across passengers.
To hold 3,800lbs + the weight of the truck, those tires probably would have needed to have been inflated to their max PSI, if they could have to begin with. I mean 3,800lbs + half a truck is 3/4ton territory, we're talking thick E-rated tires running 60-80PSI. That is what an OEM would want for that duty. A P-rated tire running nowhere near that? Oof.