I'm just really confused that I have 4 tires with payloads of 2601 lbs each yet I can only load a total of 1218 lbs on my truck when the truck manufacturer says I can load 1485 lbs.
You can load another 1218lbs on the tires, on top of the weight of the truck, which is already carried by them. This will bring you to your GVWR. In short, if your GVWR is 6800lbs then your trucks curb weight is 5582lbs, leaving you the payload of 1218lbs. Of course the tires have to be rated higher than that for some safety margin.