i just tackeled this prob with my 454.....but mine turned out to be a bad valve guide......but the main problem was timing....bad gas mileage?.....hesitaion?....but higher RPM's she is all there right?....
but what kind of ignition are you running?
vaccum advance dist.?, coil,?.....MSD?

pull the plugs and see if there are signs of detonation (small black spots on porcelain)

and if they are fouled that is fairly obvious

but i had my initial set to 10....and i thought that was to advanced.....so i went to 12 and it cleaned up right away.....

check the timing advance as well....i had a bad diaphram and that would make the car run really crappy off idol.


you have already thought of all this.....but it got be back running.....hopefully it can help you