I'm aware many are coming from V8's and V6's with much more power. I'm not. I drove VW 4-cyl 5-spd TDI Diesels for 20 years of my working career ~110 mile R/T commute, before I stepped up and bought a Grand Cherokee Eco-Diesel in 2016. What I can say about the 4-cyl diesels, is that no matter how hard you pushed them (85-90MPH), the fuel economy rarely suffered. I have hundreds of spreadsheet logs from my weekly fuel purchases showing my fuel economy was routinely 44-46MPG at those speeds. A gasser 4-cyl, on the other hand, does not have the capability to continually deliver fuel economy at 80-90 MPH. Especially in such a large, heavy vehicle. In other words, I think 24MPG is attainable without a roof rack and keeping the speedometer under 65.