[Jackpine]

Head wind will absolutely KILL your gas mileage. Let's just assume you had a tail wind of about 5-10 mph on the way out. On the way back, if that turned into a 5-10 mph headwind, it would be kind of like driving 10-20 mph faster, as far as wind resistance goes, and, because drag increases with the square of velocity, the drag you would have to overcome would increase enormously. To give you some numbers, at 70 mph, the velocity effect on drag is 10,540 feet per second squared. At 80 mph (or with a 10 mph headwind), the velocity effect is 13,767 and with a 20 mph headwind, the velocity effect is 17,424. A 30 mph headwind at 70 mph gives a drag effect of 21,511 - over twice what it was at 70 with no wind!

Over a period of 1-2 weeks driving on trips, I average about 12.7 using Bill's tunes pulling our trailer (for the whole trip). But, individual fillup calculations vary anywhere from well over 14 mpg down to below 10 mpg. Some of this, of course, is downhill vs uphill, but wind plays a big part too.

Did you program the Level 2 tune without opening the Custom Options menu? Notice I said opening! If you didn't open that menu, then your Tire Size and Gear Ratio were set at what Ford put in the PCM when your truck left the factory and should have matched the stock tune values. But, if you opened that menu, but did not set BOTH the TS and GR to correct values manually, then one or both is almost surely wrong, which means your speed was different.

And, if you were fighting a headwind, your TC may have been unlocked more often.

As Cody says, either calculate the mileage using the two tunes going the same way at the same time on the same day (impossible), or, average the economy using the different tunes over a 1-2 week trip driving essentially the same route in essentially the same weather and at the same speeds.

- Jack