My dad had a 86 E150 short wheelbase van that had the 300 and a automatic overdrive and it got aroud 21 MPGs on the highway so I figure I can get similar mileage doing the same with the 70. His van was a conversion and probably weighed about the same as my F250 so I might be able to get decent mileage from that combo and this truck does not haul much mainly brush to the dump and a engine now and them plus I use it for junkyard trips. Years ago I had a 67 C-20 with a 250 and 4 speed with 4.11s that got 18 to 20 on the highway,now that was with the 55 MPH speed limit but I think I can coax some better gas mileage from a six and a automatic overdrive for highway cruising.