I am getting 8.5 to 9.5 depending on speed. I weigh in at just over 26K lbs. I can change my fuel filter and replace the water separator in under 15 minuets.
What is the real diff in MPG's? A couple or several? The 450 will yank a higher payload and trailer than any 350 series. Have read that the 450 has a tighter turn radius. How easy is it to get to fuel filters if you do your own changing of them? I have owned Ford SD since '03 and have been happy w/ them. Always have a special place for GMC probly cuz that's the 1st truck I owned ('72 4x4, 4spd, 350 w/ 4 barrel, manual steering), then bought a '86 6.2L diesel and later a '91 after a '88 Ford w/7.3 N/A. So while I like the Ford line, I will say, the new Rams are sharp looking. IMO, best grill yet in Ram line up. So OP, your best bet is to sit in each, take 'em for a spin and see what you like/dislike about each. We can ALL give you our take and point/counterpoint each other as to why we think our brand is the best (honestly, they are all good), but only you can answer that.