Isn't this similar to what happened with Ford and their power-stroke diesel engines back in the 90's? At that time, they had a very good engine, but then due to some issues with Cummins, they went out and created a new engine that was horrible. It's taken them almost two decades to come back and offer a quality diesel engine.
Case Construction equipment used to have Cummins engines. My dozer has the Cummins 6CT 830 engine that only Case can sell parts to. If you go to a parts store like Napa, they ask for the serial number and then tell me that they can't find any parts for it. Fortunately, Case is cheaper then Napa for parts. I thought that the Cummins engine was a good reason to go with Case. But once again, issues with Cummins led Case Construction to go with Isuzu engines instead of Cummins.
I'm not sure what's the deal with Cummins, but hey seem to be losing a lot of business selling engines.
If I was looking for a new diesel engine truck, I don't think the Cummins name on the engine would make a difference for me, it would be all about history and what others have experienced with them.
I think Cummins gained a huge boost in name recognition by Dodge, and later Ram in their advertising and promoting it as the best of the best engines. It's all marketing.