Why would you guys want to alter the stock fuel/timing while the engine has no modifications? Normally, if you pull out the fuel, the timing is advanced and that's not a good thing. But if you carefully tune it, then you might gain some hp. That's what most aftermarket ECUs do with stock engine. However, it costs like $1000 or more for this, which I don't think is worth.
My experience was that I took my ECU from one of my Hondas (stock engine) to JETCHIP and guess what, they gave me some misfires along with damaging the cylinder walls. After that, I don't trust any ready re-programmed ECUs, unless the programmer put my car on the dyno, hooking up all the sensors, monitoring it and tune it. You can see many programmers advertise that you can send in your ECU for a re-tune. That's very risky because every car is different based on its mileage and condition of each car, although the tuning was tuned on other cars with the same model/year.
So before you do this, ask yourself a few questions. How do you know if the ECU is still in specs, fuel injectors working properly, combustion chamber is cleaned with no damaged pistons/rings/walls...etc? How about other sensors?
Again, if you really care for the gas consumption, this V8 is not a right choice. The V6 might be a better choice. But if you look for more power, then this V8 maybe the right choice. Power and gas consumption are always linear. You may ask David (Lextreme) about his turbocharged LS400 or Jibby about his NOS SC400, they'll show you how powerful their car are, but also show you how fast the gas needles drop down after each rev.