We went through this when the 250 was released too. Nobody has been able to clearly or reliably explain how the "Tire and Loading Information" load rating is calculated, or why it's several hundred pounds different than the conventional way of calculating payload.
I recall that
@cruiseroutfit did make an inquiry with several people who would know (thank you, again); those people reported, if I recall, that it involved a complicated and inconsistent mix of factors.
That leaves us (or me, at least) with the conventional (longstanding) payload calculation, which is as follows:
Payload = (Gross Vehicle Weight Rating) - (Curb Weight)
700h OT: 1,505 lbs
250 1958: 1,365 lbs