New tow vehicle...6.4 hemi or Diesel?

I have a 2017 Ram Crew Cab with the 6.4, 4.10 gears, 6 speed auto trans. It was a big improvement over my 2007 5.7 hemi. I tow 35 miles to the track, and have 3 "hills" on my route. My trailer is 24' and only about 7,000lbs loaded. The truck does see about 4,000 rpm towing up the hills going 60-65 mph, but it has enough power to keep pulling if you want to go faster. I avg 9-10 mpg towing and 13-14 mpg with no trailer. The new 8 speed should be a tad better I would think, but don't have any experience with them. Wife and I bought a 2020 Ford V10 24' Class C motorhome this year to use. Just filled it up this weekend and we are avg 6.5 mpg for that towing the same trailer.