Interesting thread and figured that I would chime in. My 2017 6.4 3500 with the 6 speed trans is just now approaching 50,000 miles and I have been very happy with this truck. Bought it new so I know all of its maintenance history. Really the biggest issues that I have had with it are the recalls, especially the drag link recall. Initially I got the welded jamb nuts "fix" but after I insisted to Ram Cares that this "fix" was completely unacceptable, I now have the updated drag link installed.
About 18 months ago I got a repeated misfire code on cylinder #3. Each time I cleared the code it would come back within a couple of days or so. The engine always ran great during these episodes so I was sure it was just a "phantom" misfire code. At any rate, I ran a bottle of STP Fuel Injector cleaner through one tank of gas and haven't had a misfire code since. Coincidence? Perhaps, but the bottom line is no more CEL's or codes.
Other than these minor issues, I have had no problems whatsoever. And this truck works HARD; it carries a heavy camper (about 3,800#'s) 98% of the time on the mountainous and not-so-perfect roads of Alaska, sometimes towing a light trailer (1,600 #'s). It is not my daily driver so a vast majority of its miles are highway miles.
I am running Amsoil in the engine, transfer case and front and rear differentials. I never push the engine OCI and only once exceeded 5,000 miles. Most of the time I don't exceed around 4,500. Am I throwing some money away using this interval? I'm sure that I am. Do I care? Absolutely not! As has been pointed out in this forum, oil is a lot cheaper than engine parts.
Front and rear diff oil were changed at around 16,000 along with the transfer case using OEM fluids. Then again at around 40,000 with Amsoil. I figure that these fluids are good for quite some time. I had the trans serviced at around 30,000 and OEM fluid was used as I had this service done at the dealer. Will have it changed again when I get closer to 60,000.
I changed the brake fluid at 3 years (2020) and plan on changing it again within the next few weeks.
In summary, the truck drives great, has plenty of power, the cab is very comfortable, and so far has been very reliable and trouble free. No regrets with this purchase whatsoever.