One way is to increase the Efficency of the engine via timing or removing Slop from the trans.
The trans Slop is the easiest to fix. Remember though, the more line pressure you run, the more loss you have due to the trans pump being harder to turn.
Shifting patterns play a big role in the way the vehicle uses fuel. Think of this, When a car goes up a hill, and you see yourself having to press the TPS to 50% or more and the car just boggs down and you keep pressing it in more, Would it have been better for you to just allow a lower TPS vs Downshifting pattern? So as you go up the hill it just either unlocks the converter or performs a downshift to the previous gear. Now the vehicle will climb the hill with ease. You will see that the injector pulse width "Fuel used" will be much less as you climbed the big hill.
Another route is to use the Custom os3.