urq leaning out after boosting

[GMBCHEF at aol.com]

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  Greetings.
 My urq is still leaning out after it warms up and seems like ONLY after I
boost it and redline it a few times. All switches and sensors new, including
O2 sensor. Vacuum gauge is at 15 at idle. Stalls immediately after removing
oil cap.
 If the duty cycle is at 45%, it will go up to 95% after driving it hard, and
will stay there until I turn the screw again, even after sitting overnight.
If I just putz around town, the duty cycle stays put. I've checked the
injectors to see if they may be the culprit by letting air sneak by, but they
seem to be pretty tight.
No idea here! Otherwise the car is running pretty darn good and strong!
Thanks
Gary