It is true that your ecm must readjust to the new air fuel ratios , not sure about exhaust but it makes sense, as far as it taking a few tanks of gas to adjust that seems a little long to me, one way to cure that is if you change anything, simply disconnect your battery, wait about an hour, then reconnect it, this will reset your ecm and it will adjust right away to whatever changes you have made.
This is the information I was given when I changed the intake on my vehicle, as far as waiting a full hour I am not sure if that is necessary or not.
One thing for sure though is that no exhaust on the market today that is street legal is producing a 25% increase in fuel mileage, that is just a lie, and like I said earlier I bet you cant get one of the Aero Dealers to even guarantee a 5% increase in fuel mileage with the aero exhaust and I challenge anyone to produce a dealer who will.
