If it is an option on the order sheet to delete those items then that truly is the maximum payload capacity of any version of that truck available. You can then use that in advertising. That is no different than using the payload numbers for a short cab 4x2 with the v-6 in an advertisement. It is the consumers and dealers who are embarrassing. They just assume since one version of the truck has x payload capacity that their loaded crew cab 4x4 must have the same.
It is so simple, take GVWR and subtract your actual weight (not curb weight) this is your payload and actually has to be done at a scale. The advertised numbers are ideal and do not include options.
It is really a lack of education of truck buyers that leads to this since the payload of a half-ton truck can range from like 3,000 lbs down to less than 1,000 lbs if you add enough options.