Are y'all driving with your e-brake on? My wife averages a hair over 25mpg on her new route to work, and it's mostly traffic.
I don't see how anyone can be below 20mpg under ay circumstances unless you are in snail-pace stop and go, uphill, both ways. It sounds more like driver input error or incorrect math. It also seems that the mileage really doesn't get much better until after you break that 6k mi mark.
When we initially bought ours the mileage was in the 19.5-21mpg range for the first 2-3k miles, and then eventually went up to where it is now. Maybe fuel blend issues are the problem is some areas as I noticed a mojority of our members are in the great white north or close to it.
What brands of fuel do y'all use? I stick with Shell, Chevron, or Exxon, no discount brands. When people say "they're all the same," They're not and it comes down to what additives are used. $.03 per gallon is not going to make me put cheaper gas in my car that can cause valve and injector issues, which directly affect fuel mileage.
I get 15mpg out of my old diesel work truck, which is what it was supposed to get when new, 22 years ago, with 200k less miles on it. I only drive it about 5k miles a year, and I keep up with the maintenance, along with not trying to drive it like a racecar.