I had not heard this. I've driven about half a dozen of them as rentals, both standard and Rubis (all 2 doors, because Jeeps only have 2 doors from where I stand!). Most of what I've heard about the motor has been positive.
I've got a friend who just picked up a 4-door Willies Wheeler. It will be interesting to see how things go with it.
The motor itself is just fine and deserves the praise it gets. The various transmissions it's attached to in the JK, Journey, WK2, etc. are all **** along with the electronics controlling. Getting a 14 MY to 10,000 miles or 12 months of ownership without qualifying for lemon is rare. Chrysler group's attorney's are overwhelmed, they have a flat out denial campaign in their service drives to try and minimize their liability, and as a result the internet forums and service lanes alike are rage filled.