I own a 2019 RAM 3500 6.7L HO Cummins with the Aisin transmission. Its a nice engine with good power; the transmission is durable but clunky and slow shifting. Compared to my 2017 F-350 with the 6.7L Powerstroke, the RAM is slower and if anything gets worse fuel economy. Its also harder to service - and that's not the fault of the Cummins 6.7L since its used in other applications - but the oil filter is in a terrible spot on the pickups and so are the fuel filters. A modern Ford 6.7L is effortless to change the oil and fuel filters. Duramax is pretty easy too. And if you watch any of TFL Truck's comparison tests towing max loads up the Eisenhower tunnel pass in the rockies, the latest Powerstrokes really outclass the Cummins trucks. Considerably quicker and better fuel economy. Will they last as long? Who knows. I also still have two Ford 6.0L trucks, a 350 and a 550. That V8 diesel was made by Navistar and known for its problems. But once you fix them, its a great engine and I like it better than similar-vintage Cummins 5.9L 24V engines. More power, much more responsive, just not as good of fuel economy.