final attempt to fix gas mileage...

Well it's been a long journey and i haven't seen any improvement of my gas mileage. To start i get about 10 miles to the gallon. For example ill put like 8 gallons in and at about 80 miles i have to fill up... the weird thing is i can drive cautious and slow acceleration or i can be just pedal to the floor half the miles and i seem to get the same mileage...

so i have changed the O2 sensors, swapped MAF with a friends 5.0, check fuel pressure regulator and it isn't leaking, checked all the other sensors, ran seafoam, ran lucas injector cleaner, checked timing, experimented with different gas and grades. And my car doesn't pull any codes...it's really weird... I can't figure out what is wrong. I checked my fuel pressure and it's good. Changed fuel filter nothing. I don't know where else to look

Anything else i should be looking at.

Since i bought the car it has been the same... I did a complete tune up when i first got it but that didn't help. The tune up was probably 7-8k miles ago...I did plugs, wires, cap and rotor, fuel filter, oil and filter, cleaned TB, MAF, IAC, ECT, just about everything. But it didn't change anything. The only thing i haven't done is physically take the motor apart. I tried SEAFOAM but do u guys think there is something better out there? Like GM top engine cleaner, or engine restorer, or that gunk engine flush..?

Well if there was aftermarket gears put it they sure aren't a high gear...because i've driven a 5.0 with 3.73's and it's totally different than my car. So i dont know about the gears. Yeah my car was just aligned and i think im running 38-40 psi in all the tires. As for the brakes...im putting in 4 new rotors and all front/rear brakes this weekend so i guess i'll see if that does anything, lol.