Some people claim that at WOT, the stock ECU does richen the mixture way too much (like 8:1). I'm personally not convinced, especially if you're flowing more air with your CAI and cat-back. Bear in mind that you need a richer than normal mixture at extended periods of WOT to keep combustion temps in check and for smooth power delivery, but that is not always the best mixture for power. Check to see if your throttle stop is letting the throttle plate travel past WOT (where it is 180 degrees to the air flow), and is actually starting to reclose the throttle. I had an old Mercury that used to do that. If that's not the case, and your car is actually making more power at 3/4, then it probably has something to do with open loop vs. closed loop operation, and could indicate another problem that the ECU is working around in closed loop operation, like an out of range coolant sensor for example. Often a sensor can be out of range far enough to affect performance but not set a code because it is still working, and therfore th ECU has no way of knowing it is out of range.