Advertised Payload by manufacturers are always a bare bones gasser. Usually single cab/smallest engine 2wd with nothing in the seat or bed. Once you start adding cab, powertrain, and bells/whistle configurations this payload number drops depending on your choices. Hence why a fully loaded 4wd mega will have the smallest PL# and why the door sticker is so important.
Then it gets worse. Start adding people, tools, campers, or any type of gear for work or play, you will get to zero or a negative PL# real quick.
Diesels are meant for towing, if payload is your nead, then a gasser is the best option. If you need both, then estimate your max carry outside the truck (camper, tools, wood, gear, animals, people, etc…) and that’s your magic number for in vehicle weight/payload. Most will need a 3500, some will need a 4500 if the Cummins is a must.
I have a 2500 6.7 but I carry most of my weight in a trailer and keep my truck fairly empty.