Yes, give it up!

When people ask me how many mpg's my truck gets, I just tell them I have no idea, since I can't really influence it anyway.

You'll spend more money on gadgets trying to figure out how much gas you're burning, and hence the most efficient rpm to run at then you could possibly save over the long haul. Modern fuel injected vehicles are relatively efficient. Lets say somehow you could save 5% at the max in your fuel consumption, so what will that be, $2-3 a week? Maybe in 5 years you could break even on a fuel meter. Also, unless you get something really accurate, your data won't be good enough to let you realize any fuel savings.

If you want to save fuel, then there are some basic things to consider. Accelerate smoothly from stops, stomping on the gas will really suck up the fuel. Draft behind 18 wheelers on the freeway, ok maybe not recomended, but it definately does cut back on fuel consumption when the vehicle in front of you is moving the air out of the way for you. Cut back on your short trips around town.

Pecos
I'm glad to see that I'm not the only one that get's into those "deep thoughts and problem solving" when driving.

Will
I am glad I am not the only one who doesn't know what his mileage is. I'm not going to sell my truck because of the mileage anyway.