what kind of mileage is poor? what's your drivetrain like? 4 speed, 5 speed? i may be wrong about this but it's my understanding that when you go WOT any and all adaptivity from the ecu goes out the window and it runs basically full fuel demand, obviously mitigated a bit by the fpr. i have an 81 zxt motor in my 77' and i get black smoke when i get on it. a little isn't necessarily a bad thing. i would be more worried if it was affecting driveability. the fact that you seem to be getting normal A/F ratio's under all condition aside from WOT would make me think everything's working just fine. 10-12:1 is where you will make the most power from my understanding.