I used to get mid 18s with my 15 powerstroke but honestly I dont miss diesel at all... I always used additives for it between that, draining the water from fuel filter monthly, 13 quart oil changes and the up front 9k premium for me I would have had to drive it close to 200k miles before it paid for itself with the increase in mileage since diesel up by me has always been well over 50 cents higher than even mid grade.
Not to mention all the epa crap on those things anymore and if you need to replace injectors or fuel system its big $$ thats why I went to gas. Dont get me wrong though having that 900+ ft lbs was fun but just not worth it to me.
I dont know, to some this is a very good point and must be considered.. Is it worth it to you?
My son had a 2013 f350 6.7.. It was an emissions nightmare. He bought a new 2017 6.7 dually and put 42K on it the first year and it has been problem free. He is a pipeline welder so it gets beat on, mud, rocks..2700 pounds of welder and materials in the bed everywhere he goes.
For me, I did o.k with the 6.4 gasser, and overall I cant really say anything bad about it. That gap between 1st and second gear was annoying though with a heavy load.
I had personally been researching the diesels for about 6 months, and when my trip to WV had me downshift from 4th to second at 65 MPH and then the rpms jumped to 4700 or so, thats when i started taking a hard look. I also found myself not even contemplating some of the campgrounds up in the mountains near me simply because, even though I knew the truck would pull it, It wouldnt be an easy pull.
At that point the truck I drive was dictating where I was going to tow my camper and I was missing some good spots. So Yes, by all means folks need to do some soul searching.