I have owned 2 different Chryco's with the 4.7 and I love that motor. I have had no major problems out of any of them. The Durango had 176K and still pulled down 25 MPG and the WJ has just under 100K and gets 24 MPG with a BB and bigger tires. I had to replace the water pump on the WJ at 35K under warranty for a bad bearing. Other than that that is the ONLY maintenance replacement part I have put on either of them. The WJ is probably do for spark plugs by now. If I could have found one for Betty you can bet it would have made it's way into the truck before the dinosaur 5.2 Magnum did.
I would never, ever, own a WJ with a 4.0L in it. The Jeep is too heavy for the 6 holer.