I just got back from a Jeeping trip to Windrock Park, near Knoxville, TN from Detroit, MI area.
Overall I was very pleased with the performance of the 6.4 Hemi. It pulled the hills in KY and TN just fine. The rig's gross weight was 20,020 with both driver and passenger in the truck, Jeep, parts and gear in the trailer. Gas tank was full. CAT scale weight.
I will update the exact stats in the next couple of days.
It's never gonna be a Cummins, but those days are behind me. For a daily driver with occasional towing duties this suits me just fine.
EDIT: 1098 miles, round trip. 154.251 gallons used = 7.118 mpg. Lie-o-meter said 8.2. ;-)