The Mean Elevation of the state of Missouri is 800 feet above sea level.
The Osage Plains cover western Missouri. This area is mostly flat but some hills are evident.
http://www.netstate.com/states/geogr..._geography.htm



you have to remember,some of us are not so lucky to live on such flat ground,and simply will never get that kind of fuel economy.
what size tires do you have and is the odo accurate? how has it been verified?
just curious.that seems too good to be true is all.
very good numbers,and please don't think im calling you dishonest.just always good to get all the details we can so when we make mods to achieve increased economy we can learn from you.
if you can,please fill up and note the fuel economy on the the next tank too please.this will correct any fill up errors.

 

Unless you fill at the same station, parked the same way and fill the tank exactly the same every time, a MPG number from one tank of fuel is rarely an accurate number.

Write the miles driven and gallons burned for at least 5 tanks of fuel, then your numbers will mean a little more and be much more accurate.

If I look at my spreadsheet, my 13 year numbers look like this.
Jan. 1, 1997 to Dec, 31, 2010, I burned 16,051.45 gallons of fuel.
Kind of interesting, average cost per gallon of fuel over that time period, $2.101 per gallon with an average fuel cost of 21.9 cents per mile.

Absolute max MPG 28.6
Absolute worst MPG 2.9
Average MPG 10.31

Last time I got over 20 MPG max under normal conditions, 2001.
Last time I was over 17 MPG, 2005
Last time I was over 14 MPG, 2007

My guess is the 28.6 was when I pulled out one of the fuel tanks, so that threw my mileage off at the next fill up.
Likewise the 2.9 was probably when I put the new tank in, so all that extra fuel, 44 gallon rear tank sure dropped the MPG numbers.

This year the only times I have driven my 86 I was plowing snow.
So my average for this year is 3.47 with a high number of 3.66 and a low number of 3.10.

Since I use mine for business use, I get a cash receipt for every fuel purchase and the odometer mileage is written on each receipt.
Those get entered into the computer along with any repairs or upgrades to the truck.

Makes it easy to calculate one tank, one month, one year or 13 years.

Also one more interesting fact.
Total operating cost for 13 years, engine rebuilds and all repairs included, almost enough to buy a 2011 F350 with most of the options.
$64,515.16

Pre 92.5 trucks most likely do not have accurate speedos, even with stock tire size.
If you are not running 235/85-16 tires and the speedo has not been re calibrated, the mileage you are using to figure with is most likely wrong.

Look at a truck that is burning 16 gallons of fuel in 240 miles, 15 MPG.
Same truck, 10% speedo error to the fast side (6 MPH at 60) and that looks like 264 miles on 16 gallons, 16.5 MPG.
Same truck 10% speedo error to the slow side and that gives you 216 miles on 16 gallons, 13.5 MPG.