Have you checked the total advance(vacuum advance plugged,3000-3500 rpm)?Total should be limited to 34-36 on pump gas,but there are always cases that contradict this.Quite often the setting that produces the most low end torque and throttle response is too much at wide open throttle,and it can detonate under full throttle,even though you don't hear any pinging.I don't know how much mechanical advance your distributor has,but most stock distributors need the cam rotated to the shorter position to run that much initial advance.Check it out with a timing light and let us know what you find..