I think you’ll be hard pressed to find many of us with a Hemi getting over 20mpg at 75mph, to be honest.
I haven’t done anything to help fuel mileage with 33” aggressive tires and a lift, but I’d be happy to see 16-17mpg on the highway. My truck never saw over 18mpg in stock trim.
Anyways, I guess my opinion is not to buy a Hemi if your only goal is to improve fuel economy. Hopefully you find enjoyment in other aspects. I’m really happy with my Ram selection, but not at all based on fuel economy!