Begin with the idea that the Body is the Rotor in a Centrifugal Motion whose model (and ultimate perfection) is the Gyroscope . . .
Two words come to mind . . .
Ben Hogan
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"In my experience, if you stay with the essentials you WILL build a repeatable swing undoubtedly. If you can master the Imperatives you have a champion" (Vikram).
The reason you can't sustain the lag is because you are so eager to make the club move fast (a reaction to the intent of "hitting it far"). So on a full shot you throw it away too early, which doesn't happen for your short chip. (bts)