Mileage of 6.4 Hemi

I had one of the 3/4 ton gas trucks (2015 Chevy 2500HD SRW with the 6.0L and 4.10's) I commented in another thread that I got 8.0-8.5 MPG towing a 9,000 pound travel trailer. I now have a Ram (2017 3500HD SRW with the 6.4 Hemi and 3.73's) and tow a 10,000 pound 5th wheel. My average mileage is 8.5-9.5 mpg. I've towed the same routes as I did with the previous truck. The only thing I can't account for is whether I've had any different head/tail winds but I'm going to assume they have been similar. So with a little heavier RV that's a little taller but has a more rounded nose I'm getting a little better mileage with the Hemi. Not an Apples to Apples comparison but I'm happy with the results I've been able to obtain.