Forgive me for being ignorant.....
If I install an adjustable fuel pressure regulator with other injector mods, I KNOW that I can turn the pressure UP for a little more performance (more gas), BUT if I turn it DOWN, will it help mileage ?? if so, how much ?? better than stock ??

 

You can theroetically improve gas milage by decreasing the amount of fuel you put into the motor but then you are leaning it out which is bad for everything. It'll overheat the cat, cause deposits in the intake, burn up spark plugs, ect.