Realizing that the OP asked about 3-4 year old trucks, I'll put in my .02 anyway. As seen in my sig, I had a 99 QC 2500 Cummins long bed. About 5 years in, maybe 40,000 miles, my fuel lifters had gone out, forcing my injectors to take up the slack and then they went out. Forgive me if my terminology is muddled as this was some years ago and I'm not a mechanic. This required about $3k of work to resolve. I am not handy with a wrench, so had to use a diesel repair shop.
The 2500 2wd with .410 gears did a credible job of pulling our 5'ers though mountain driving often required me to go to 3rd gear. When pulling the 27' Forest River, it wasn't bad, but the 31' Sunnybrook was a lot heavier and often I wished that I'd had more power. The 8' bed was roomy, and I used the room, mostly for stuff that I didn't have time or room for in the 5'er's storage.
I would imagine that, since the QC isn't available anymore in the RAM that a CC with 8' box would be quite a beast, but it is what it is.
Personally, I don't care about the storage lost by going with a 6' bed, but I would like to know what hitching/unhitching, and pulling differences, if any, are to be had with a 6' vs. 8'.
It is also my plan to buy a 2-3 year old TV in 2016 when I retire, so I'm deeply interested in this thread.
Thanks!
DShizzel