I have a 1999 GMC diesel, 6.5 Turbo.
I get 17 to 19 MPG depending on the road conditions. Weight does not seem to really affect it, loaded at 3000 lbs I got 17.5 and on the same road with 400 lbs I got 17. My mileage is lower than others; I drive my van at the speed limit, not at 55 or 60 as...