It's due to oil blowby and soot and carbon build-up on the valves. They have a new valve that is supposed to break up the hard carbon build-up during normal operation. All part year and newer 2015 engines already have the update. All US older guys out of warranty must create our own system to stop the oil from entering the intake all together.
Battling Chrysler for this exact issue right now on my 2014 eco-diesel that I bought in July 2014. I’ve had it in six times now for the intermittent shutter while going up a slight hill at 40 mph. Each time they do a regen On the exhaust system and they changed out the fuel filter and clean the fuel injectors. The technician I’m working with wants to replace the cylinder heads but Chrysler is fighting them on it. Also dealing with a very sluggish acceleration off of a stop. Takes the turbos about 3 to 4 seconds to kick in and then the truck has a significant forward lurch, makes it scary pulling out in traffic. All of the stuff came up after I let them in stall the eco-diesel recall.