So I was getting horrible gas mileage, like REALLY bad, and I had some stuttering and hesitation around 25-40 MPH. I replaced the mass airflow sensor, which did not give me a check engine light or a reading code from a diagnostic test. I changed it anyway. I also changed my plugs and plug wires, and cleaned my air filter, sprayed out the air intake, and cleaned the throttle body out real good. I also sprayed my sensors with some sensor spray. After all that, I am pretty sure my gas mileage has doubled. Maybe not actually doubled, but damn, it's waaayyy better. And the hesitation is gone. Runs like it's brand new, I'm lovin it! If you want details on how I did any of this, feel free to ask. I have a 99 SR5 3.4 V6