I live 15 miles from nearest small city and an hour from larger ones, in the Shenandoah Valley of Va. I seldom ever use I-81, preferring US Rt 11 and it's lower 55 mph limit and lighter traffic and no back ups due to crashes. I worked as a Trooper for 31 years and so avoid Interstates ..... though I do like that they keep most traffic off my favorite roads. I also still like spirited driving at legal speeds but I always did .... I just don't feel the need to run 100 after so many years of sometimes hitting 130-140 maybe several times a day or for many miles. I like cars, I like to drive, I like to see sights, visit history, to see history even in old roads / motels / resturants / roadside attractions, etc. It's like a hobby.
The secret to good mileage is anticipation of slow downs, hills, stops and a steady foot ..... and a willingness to let speed drop a little near top of hill and keeping revs low, get into 5th by 50.
My 2007 F150 FX4 Flareside Super Crew has 3.55 gears and a 5.4 with a SC FP 1865 tuner and cat back and I can get over 20 with it no problem ..... just using a steady "non aggressive" throttle. One stretch from Commerce Ga. to Hillsville, Va. was 21.4 mpg.
In 2006 the "Wife Unit" and I took our 2001 Mercury Grand Marquis (4.6, dual exh, and 2.76 rear gear) , our dog, cloths, cameras, laptop, etc and went across country, 21 days, 7,955 miles .... and overall average was just a hair over 27 mpg (I have the records in a book, that trip and others) and we took a lot of cloths, that trunk was full of suitcases, bags, etc and I had a few tools and stuff. I carried a few lbs in the air lifts to keep her level. We did Rt 66 westward from St Louis to Bakersfield and visited Yosemite, Sequoia, Yellowstone, Rocky Mtn., Grand Canyon, Painted Desert, Petrified Forrest, and smaller parks, Monument Valley, Gouldings, and back and forth across The Rockies a few times (I kept thinking of new things to see while we out there) and other high passes .... and a lot of 75 mph running steady out west. I was really proud of that mileage.
The 4 guages in the 2005-2009 was part of a $4xx interior upgrade package on the deluxe (which also included aluminum finish on the steering wheel and dash, and MyColor). Starting with 2010, that package was no longer available stand alone (base trims can't get it, it became part of standard equipment on premium trims).
It is not that difficult with these cars. I got behind a slow moving line of cars going 50 mph for about 20 miles once right after leaving a gas station and resetting, and I averaged 35 mpg over that time with a 4.6L 3v. My 2011 5.0 will get 30-31 mpg with the cruise set to 70 on the interstate. These cars can be surprisingly efficient once you settle in on the highway in high gear.