Sorry 300 - without a common terminology and a more descriptive post, you're kinda stuck with one band leader. One of the really nice things about TGM is there is a common terminology that can be understood across instruction circles.
If your instructor used terms like "arc of approach" folks here might be able lift some fog.
Would like to help but based on your description, there isn't much to go on.
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Bagger
1-H "Because of questions of all kinds, reams of additional detail must be made available - but separately, and probably endlessly." Homer Kelly
I've always thought finishing around the body is better for correcting a push shot. If the pull is caused by a close clubface (it can happen to a degree) then you may very well be on the right track. Does it usually draw too? If the problem is caused by an incorrect downswing plane (my personal guess without seeing anything) then you need to work on your downswing much before you work on a flatter finish.
My other guess is if you don't trust your instructor he/she may very well not be the instructor for you.
Matt
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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)