Sorry not anal enough to keep stats I had my van chipped when I first bought it my 2.3 Bessie 7.5mtr long drives like a car I'm heavy footed so mileage figures vary wildly over 30mpg when crawling around touring but early twenties when travelling, would expect that unless your planning a lot of long mileage trips the cost of a good rewrite would take a lot of recovering as most of the advantages come from torque gains acceleration and top endperformance, of course there are fuel savings if you adjust your driving to suit,