Light weight campers and fifth wheel
Keep in mind that manufacturer tow ratings are designed to sell trucks, so (at least in the past) they were a tad misleading. It used to be (and may still be) that tow ratings were for a truck with NO accessories installed, NO cargo, NO passengers, just the base truck, a 150 pound driver and a bit of gas. And that is assuming a 'tow package' which includes both a big transmission cooler and appropriate rear end gears.
Furthermore, especially for smaller trucks, it is for a trailer, not a fifth wheel. 5ers usually add 10 to 20% of their weight over the rear axel of the truck, which can often cause you to exceed the GAWR of the rear axel. Also, them hitches ain't light either...
I have (or had) a light Terry 25' 5ver with one manual slide which my 1500 chevy with the old 350 engine was supposed to be able to tow. I figure it was about 6500 pounds loaded for travel. Pretty much towing it home from the dealer told me I needed more truck for it (rear was way down, and pretty sluggish acceleration). The 2500HD is rock steady pulling that weight trailer, but even the bigger 6.0L gas engine struggles getting it up a hill.
Whatever combination you end up with, before you go out on the same road I am on, please take it to a scale and verify that you haven't exceeded the trucks GVWR and GAWR of both axels, the trailer GVRW, and the trucks GCWR.