Had a few. Always got better MPG in a HEMI. At least the 3.7L has a 5speed in the Xk.
Had a few Durangos too. Same with MPG, was better with a HEMI. I liked the ride and visibility better than the Xk. But they are butt ugly.
Typical brake issues on the D, blew out a power rack on the D. Never broke anything on an Xk.
Keep in mind high mileage Hemi engines will probably need plugs and I'd do a power flush on coolant and change diffs and tcase.