Its very hard to tell from just a video what's going on. I mean it helps but there isn't even any speed or G force data. I would guess that your cornering speed and entry speed is too high. You said that you adjusted your braking which is good but you need to adjust(reduce) your speed a specific point for the corner. As most people have already guessed weight transfer is the primary issue and your suspension is the primary cause. (you've already see this through the increase of front psi and decrease of rear psi), higher less grip front end and lower more grip rear) Better data will help better solve your issue, corner weights for example, or we are just going to all be through crap at the wall to find out what sticks. Get your read on with these.
Understeer And Oversteer: Adding Vs Removing Grip - Race & Track Driving (formerly Win HPDE)
Autocross to Win (DGs Autocross Secrets) - Weight Transfer
The other sections are very helpful too.
The G37 is a heavy soft luxury sedan and while you can drive any car on a track it's never going to be great.
Essentially you are going to have to make a decision do you want a comfortable luxury car and drive within it's limitations or a uncomfortable performance vehicle and find the next limit which will need more $$ and less comfort to solve. IE a money pit.
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