@pitch...
Yes...I am doing a lot of reading on all this. I am getting closer to understanding. You took me somewhat over the top with the comment "Every truck no matter the nominal rating,Eg,150/1500,250/2500 has a different rating". I am starting to see this. Really just baffles me why they bother calling them 150, etc. Should really be F-10000 or whatever for total towing capacity. So...payload (is that same as towing capacity?) is equal to truck plus rv? Here is a working example...(not that I am getting a 2015)....
Sample.
Maximum Conventional Towing=19,000 lbs
Maximum Payload=7,260 lbs.
Maximum GVWR=14,000 lbs.
Please make sense of these numbers.