A few things stand out from the OP. First, a 30' fifth wheel should be in the 10-12k range, not >14k that needs a 1-ton (dually). Shop around for your dream RV and determine the weights. Then find the truck you can pull it with. Or just get that dually now and you should be good to go towards 15k loaded.
Second, more transmission gears have changed the need for axle ratios >4.0 in the pasts several years in many cases.
Half tons have a lot of power compared to 3/4 tons from 10 years ago. They still do not on average have enough payload to handle an 8k loaded 5th wheel RVs. You'll find the needles in the haystack that a few owners on this forum have, but they are <1% of half tons sold. In order to support an 8k loaded 5th wheel, the truck needs enough payload for the 250 pound receiver in the bed, some stuff around the hitch, people and cat in the cab, and 1500 pounds of pin weight. Heck that can put a diesel 3/4 ton over it's GVWR.
