Last year we went thru this drill. We wanted a new larger 5th wheel. In the fall of 2015 we bought a new RAM 3500 CC 4x4 SB Laramie with Aisin tranny. The Aisin cuts into the payload by 150 lbs, however it is well worth the lost of that payload. Yellow sticker is 3664 and tow guide says 3920 for a CC 4x4 SB, so Laramie, running boards and other things lowered it almost 300 pounds. The Long bed is listed as having 410 more lbs of payload. And GVWR is LB 12,300 vs SB 11,700. However the Long Box is rated a few hundred pounds less for allowable trailer.
Moving onto trailers. We had our 29 foot Cardinal for 12 years and wanted a new Cardinal, however only their smallest one had a light enough pin weight for the SRW, on we went to Montana dealer to also find only that one their smallest one had a lower pin weight. What we figured out with help form the Cardinal owner forum was the Cardinal had move the axles back on the larger units thus creating a higher pin weight configuration.
We found the Bighorn and Cedar Creeks in the size we wanted both started with pin weights in the 24xx range, while the Cardinal's and Montan's were pushing 3K for dry pin weight.
So we have a 39'4" Bighorn 3575el and it matches up with the truck just fine. We towed to Arizona this year via 93 in Nevada in 40 MPH side and head winds and did not get pushed around.
The new gen trucks, Ford in 2017, RAM in 2013 and GM in the last couple years greatly increased the strength of their frames in their trucks and the result is a much better tow rig from all three. Chris