just to add my two cents I was in a 2014 3500 ext PM up until a few months ago.
I was in it from about 140k to 200k, I know it still had the original tranny and engine but idk if any replacements on anything else happened before that.
It was very solid running, but wasn't perfect, when I first picked it up totally empty coolant, turned out to be leaking coolant so we replaced the radiator (much later, we just kept adding coolant for a while since it was a small leak that didn't get worse) Then once I hit a bump on highway and both headlights went out, was explained to me it was something about the way they made the casing not being able to aborb shocks well or something like that I don't really remember.
As far as the three skids go, it was pretty much all the room in the bed, maybe like 6 inches or so extra room, also the whole time I was driving I got one of those loads. opted to sleep on top of the freight without my bed lol, not the best nights sleep.