On the 05+ cars WOT A/F learning does occur, there is no way to turn it off, you can only limit it. The way VMP Tunning tunes are set up the car should only learn an a/f correction below 3000RPM at WOT, this way high RPM a/f and power are not effected.

Normally the computer only learns in closed loop (idle and part throttle), at WOT there is no real learning that occurs. However, the computer will take learned a/f from the higher throttle areas where it is still in closed loop, and apply these corrections to the WOT area where it is open loop. This is where you could loose a little bit of bottom end WOT power if the A/F is rich or lean, though it would not hurt anything.

You should not have experienced a loss in gas mileage, unless there is something wrong with your front O2 sensors.

There are many types of learning. Long term learning can be turned off, and short term learning can be left on, to prevent the low rpm changes in wot fueling. However, even this I do not recomend as it can decrease driveability. Learning can be turned off all together and the car can be forced open loop all the time, but I don't recomend this if you want good driveability and mileage.

Justin
VMP Tuning