The bottom end is new, even down to the pistons and rings. The top end is new. The turbo, EGR system, emissions, all of it is new. FCA claimed in all of their press materials that it's an 80% new engine, and I don't have any reason to doubt that.
Even the engine pressures are different, which is why they are telling us that Rotella is no longer an acceptable oil, and the filter has been totally redesigned.
So far I've seen the typical Bosch CP4 injection pump failures, and a handful of blown engines as in 2 maybe 3. Oil leaks from the timing cover are very common. Otherwise the Gen 3 engine seems to be doing great and there are guys with 80,000 miles on them over on one of the Ram forums.