Well Skeeter I was just trying to be polite, lol. I ain’t never bought a vehicle and considered or worried about gas mileage.
IMHO, if U get a Big jacked up truck, with lift, tires, and a Hemi, why do you care about MPG??? Even on my stock MY 19 Bighorn 1500, I find 13-18 town, 17-22 Highway if not towing. BUT then, I's an old BOIRD and I learned a long time ago, if U want MPG, buy a Prius and put a "RAM" logo on it, LOL.
But it is a HEMI, LOL...
ADDED: On my truk, manual says 87 Octane acceptable, recommended 89 Octane. Since I do not have a 6.4, not sure what in manual.
FUEL RECOMMENDATION 2019 PW MANUAL:
FUEL REQUIREMENTS
6.4L Engine
Do not use E-85 flex fuel or ethanol blends greater than 15%
in this engine.
This engines is designed to meet all emissions regulations
and provide satisfactory fuel economy and
performance when using high quality unleaded
gasoline having a posted octane number range of 87 to 89 as
specified by the (R+M)/2 method. The use of 89 octane
“Plus” gasoline is recommended for optimum performance
and fuel economy.
While operating on gasoline with an octane number of 87,
hearing a light knocking sound from the engine is not a cause
for concern. However, if the engine is heard making a heavy
knocking sound, see your dealer immediately. Use of gasoline
with an octane number lower than 87 can cause engine
failure and may void or not be covered by the New Vehicle
Limited Warranty.
Poor quality gasoline can cause problems such as hard
starting, stalling, and hesitations. If you experience these
symptoms, try another brand of gasoline before considering
service for the vehicle.