Are you dead set on either a Chevy or Ford chassis? If not you might want to look at the Sprinter chassis setup. We just purchased a 2015 Winnebago View Profile with a sofa slide.
The first tank of fuel produced 16.8MPG and the second going over the Boston Mountains in western Arkansas was 15.9MPG. Now I know the Boston Mtns are not the Rockies but there is a lot of up and downs in them and some pretty long pulls. I know the Rockies as I used to live in Colorado for 27 years.
We traveled at 60 to 65 MPH with a full tank of fresh water and then some of that became waste water as it was being used. I never felt I was lacking power in it. Now we were not pulling anything behind so I'm sure that it will feel different once we get our toad car and get it behind the rig. It is a very maneuverable rig and lots of people never tow anything behind as you can drive it almost anywhere.
It is very easy for me to get out of the drivers seat and get into the back and I'm 6'1" 250# with size 13 double EE shoes.
It is a smaller size as it is only 7'6" wide. Ours is 25.5" long.
This is not our first class C and we have had many other RVs including class A diesel pusher.
We feel for the 2 of us and our pooch it is just the right size.
This is IMO
