They are. Exactly. Which is why the tow rating for a 5th wheel is different. You said exactly what I said.
So a 8140 tow rating is limited to the 10% tongue weight. A 5th wheel will have 18 to 25 % this lowering the tow rating.
This is hard to describe with a 1500, but look at the 3500 dually ratings. They will show that a bumper pull only goes to such rating. 5th wheel to such rating. The actual max tow rating is with a gooseneck. So when that 3500 says max tow is 35,000, that is not bumper pull or 5th wheel it is gooseneck ball rating.
The same goes for pulling a camper. 8140 would not be the max tow with a camper, as they are generally 12 to 15%
It would decrease the 8140 based on how much tongue weight the truck can handle.
So, we said the same thing. And I stand by my comment. You can not tow a 8140 pound 5th wheel or for that matter bumper pull. And of course the whole dang thing is changed if you have more than 300 pounds in the truck and your hitch weighs more than 70 pounds.
Why I constantly mention in all my posts...the max tow number is bogus...Everytime.
But, as I mentioned, depending what the axle ratings are...he may be able to fudge the numbers and be safe...going over rear axle rating, will lighten the front and cause issues with the axle.
Oh well,
Tow away!