how long do these engines last if reasonably maintained? how about the 8 speed transmissions? looking at a 14 4x4 with the pentastar/8 speed

 

This engine lasted 626K. He tore it down and found everything still looked good. He never changed the timing chain and that's what finally did it in.
The one problem I heard these engines have is rocker arm failure. An inexpensive fix if you catch early and do it yourself. Tons of YT videos out there
on how to fix them. Some say the issue was mostly with the early 3.6 engines, not sure if that's true. I got 2 years 52K miles on mine. Love this truck.

 

Concerning the transmission, one of the popular Mopar YT mechanics claims transmission repair shops not happy with the ZF8 speed. He claims it's because they're proving too reliable and not giving them much work.

 

Now there is a problem I would not mind having. But then, I don't own or work at a trans shop either.