One thing that the op didn't mention was the weight of his 5th wheel. What it really comes down to is how much percentage of your weight is on driven tires. In other words, the heavier your trailer is the more you need 4wd and trailers seem to getting heavier all the time. When I had a 4,000lb slide in camper in the back of a 2wd truck I didn't need 4wd at all, with a 4,000lb trailer I got by without it but it might have been handy, with my 12,000lb equipment trailer I need 4wd. One of the paradoxes is that 4wd components add weight to undriven tires while in 2wd so a 4wd truck needs 4wd more than 2wd truck does.
As others have commented the extra weight of 4wd components does eat into your gross combined weight and thus reduces your rated towing capacity, there is extra maintenance and reduced fuel economy. I have always heard the 2wd (and gas engines) trucks are hard to sell but I had no trouble selling mine and I am sure that I would not have recovered the investment. But, I do enjoy my new 4wd truck for my current uses.
One thing that I find interesting is that with Ford trucks you can only get tow hooks on the truck if you invest $4k in 4wd equipment to avoid getting stuck in the first place. So if you have a truck that is more likely to get stuck you can't get a good place to hook up a tow rope but a vehicle that is less likely to get stuck has good places to hook the tow rope. Sort of seems backwards.