mileage. the harder i try the worse it gets...

Been many years, but i seem to remember a 2000 mile roadtrip in my 68 A108 van, 318 2barrel, 3speed stick, 3.55 rear, about 1200lb load, 75mph average netting real close to 20mpg... The other side of that was my 77 D150, 318 2barrel, 727, 3.55s in a 9-1/4 rear, never seemed to do better than 12 around town and 15 on the road, load had no bearing on mileage, could be empty or have 2000lb in the back...