"Leon" wrote in message
...

By any chance did you drive through the mountains? Oddly I have always
gotten better gas mileage when going through the mountains. Thinner air
does not require as high of octane from the fuel to prevent valve clatter
and if you are burning regular elevation fuel 87 or better your mileage
could increase also. Typically gas octane in high elevation regions has
an 85 or lower rating.

Just back from a week through Colorado and SE Utah in the wife's '06
LandCrusier. I have noticed the same phenomenon this trip and in previous
trips in my '01F250 Power Stroke. Mountain driving seems to improve fuel
mileage by as much as two mpg. I theorize that much of it is due to
decreased speeds, often 45 to 55 mph vs. 75 to 80 on the Colorado, Utah, and
New Mexico interstates. The LandCruiser's trip computer fuel mileage drops
down under 12 mpg out in West Texas where the interstate speed limit is now
80.

If you're not already running synthetic oil, DO. You'll not only
increase your fuel mileage (one mpg, maybe more) but you'll change oil less
often and reduce wear on bearings, rings, valve train and the like.

Dave in Houston