I agree with r1c... Buy a real tuner, so there's an aftermarket and try it... Sell it if it is not to your liking. You'd have to save a lot of gas for the price of the tuner.
On a side note... Pulling has been most economical for me over the last 40 years with a diesel... I get 17-18 mpg in my F250 SC, in town and on the. Highway, empty or pulling up to 30-35k pounds trailer weight... Plenty of pick up even to pass and the newer diesels are hard to recognize as diesel from noise, etc. Of course buying a new vehicle is not economical either