Last weekend I did a highway mileage test and it came out to 19.3 mpg.  Not too bad.  We were driving I-5 155 miles round trip to the Roseburg, OR show.  My wife was on board and about 100 lbs. of supplies in the bed.  65 mph at 2800 steady.  Throttle wasnt steady though because there are 4 good size passes each way, smaller ones too, and two or three lengths of tight turns, resulting in a lot of power valve action.  The run was done with 100% gas.  Oil is usually 10/30 but had been changed the day before to 15/40.  No wind in the morning and afternoon brought a head wind that buffeted around the truck a little bit.  Previously the truck only gave 16.6 mpg with 10% alcohol.  I noticed that the engine temps, (165 in the morning and 175-180 in PM) were about 5 degrees warmer with the 100%.  With a couple minor tweaks 20mpg plus should be possible. 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.