Here in the Colorado foothills (6,400 feet at my house) my mileage is all over the place. A lot of this has to do with no flat terrain around. Always going up or down hill! Mileage sux going up, but great going down!
My truck has 3.55 gears so for me, slower is better.
I have found the 'sweet' spot on my truck seems to be between 50 and 60 mph. Any thing over 60 and mileage drops quickly. Over 65 and I'll loose 3 to 5 mpgs pretty quickly.
Lately, I've been using the manual mode on the transmission a lot. This is effective in keeping the truck in the higher gears where the fuel economy is the best.
All that said, with summer blend fuel, I'm averaging between 17.9 and 19.5 mpgs for my daily driving.
That will quickly go away if I feel the need to keep a beemer from cutting me off! :jester:
jammer
