If you're running more than the stock boost level on the GReddy kit(4.5lbs or so), and are using a boost dependent FMU, you WILL lean out under boost unless you have an inline pump. Do you know what the ratio is on your "boost sensitive press regulator"? If it's 12:1, which is the ratio that is usually used for stock injectors, even at 4.5lbs of boost your fuel pressure is going to be ~94psi(4.5 x 12 = 54 + 40psi static pressure). An intank pump can put out a lot of volume, but it can't generate this much pressure, which is where an inline pump comes in. If you're running anything over the stock boost level on the GReddy kit, then your fuel pressure under boost is going to be well over 100psi, and you will definitlely run lean. You can't rely on the GReddy box will handle all your fuel needs since you can only modify the duy cycle on stock injectors so much before you start maxing them out.