The Cummins diesels used in the Ram pickups have been the most trouble free of any of the diesel engines used in pickup trucks over the years. As for any diesel pickup produced after 2010 they are all much better than their predecessors. The transmission used in the Ram trucks is also excellent.
But that says nothing about other problems that can cost money such as the air conditioner, fuel pump, alternator, water pump, electrical system, and electronics. The more stuff that is added the more there is that can fail.