Just what I would do if in your shoes:
Rather than go by which 1/2ton has the highest ratings, if possible/feasible/in line with your plans, pick out the small 5th wheel you plan to snowbird in first then work backwards on the truck.
My logic: As was pointed out, Ram & Tundra have lower GVW ratings than the Ford & GM offerings. But what if you test drove them all and you really liked the Ram or Tundra the best? If the 5er you've picked falls within the ratings, would it matter one bit if a competitor had higher ratings?
Food for thought, and good luck on your purchase! All of the modern trucks are really nice so I don't think you can make a bad choice IMO.