Ill be nice and clarify your question despite the fact you told me you had a 370 and you wanted to know where to get it tuned in Chicago. You are correct, you heard about "tune drift" but if you read about it you would have learned that it is a correction the stock ecu is trying to make.
The AFC, as in Apexi AFC is a piggyback fuel solution that adapts the stock ecu fuel tables to get your AFR in the target range. Some one named it "tune drift" because they feel the Apexi AFC is tuning the ecu (which it isn't its just modifying the signal.... and it was drifting away from the settings because the two narrow band 02 sensors on the Sentra are so sensitive they adapt the stock ecu fuel delivery to adjust the compensation the Apexi AFC was making to the AFR to get the AFR back to stock parameters. So someone decided to say that their "tune" was "drifting" as in the modification from the Apexi AFC was variable since the stock ecu still had control over the fuel values dependent on the 02 sensor readings.
It is more respectful to read threads to learn about the 370 if you are interested than to post unrelated questions and compare it to a car with almost zero equivalency. I have seen your posts all over the board asking what a exhaust resonator is to how much power you can get from headers and if it makes the car louder.
