2019 Ram Rebel with 3.92 rear end and Etorque purchased new several weeks ago. Just turned around 1,300 miles. On my 4th tank of 87 gas. Most all miles so far are highway miles. Posted speed limit here in Montana on Interstates is 80 mph. At 80 I get around 15 MPG at best. I have dropped my speed most times to 70 to 75 mph to see if that helps . At those speeds I am at 15.6 to 15.7 MPG. Some suggest with more break in mileage, my MPG will get better. I am not optimistic that will happen. My last two trucks, GMC Sierra 1500 4WDs (2015 and 2018) with 6.2L, with direct injection, and factory 22” wheels/tires, driven between 80 to 85 mph on same highways averaged 22 MPG. Understand they are two different style of trucks, just wish the Ram Rebel could do better. Good or bad it is what it is.