[Backtobasics]

I think the answer lies in whom the question is from. An ecomodder, or an average driver?
For an average driver, who uses more throttle, then the common performance modifications (Intake, exhaust, and computer programming)will probably yield better MPG.
Computer upgrades are usually units that reflash the computer, and they frequently add additional timing.
Intake modifications lower air intake restrictions, and when coupled with someone who uses the throttle can have lower pumping loses.
Exhaust modifications also reduce pumping loses, which also show as exhaust restrictions.