Quote:
Originally Posted by swamper06
Your hauling around less weight. I think every 100 pounds is 1 mpg. I know in drag racing every 100 pounds is a 1/10 in the quarter.

The owners manual says 400 pounds per 1 mpg. If it was 100 lbs per 1 mph, I would get about 2 mpg when I haul dirt in the summer.
Back to the original question. Your math is probably correct but your numbers are not accurate. Your not filling up a bone dry tank with 8.3 gallons. Also when your gauge says empty you should still have a bit of gas in the tank.
What I do is fill up all the way, then take and divide miles/gallons. This will give you a much more accurate number. I have a small notebook in the truck and I keep track of all my fill ups in it. If you do it this way you MUST fill the tank up all the way or it wont work.
BTW 8 gallons of gas is about 65 lbs, not enough weight to make a difference.