Very interesting information. I can see how the computer would compensate for more air flow and richen up the mix resulting in more HP and less MPG. You would also think the computer would reset the timing as well. There are so many possibilities as to what the computer could be resetting when changing the air intake, exhaust out flow and so on.

I'm not sure I feel qualified to be messing with the factory setting when no one seems to be able to predict a consistent outcome.

With past vehicles I have owned, I have found the most reliable way to increase MPG is to use Premium fuel. In California that would be 91 octane. In my 1998 Chevy 1500 and 2000 Chevy 1500HD (it was a heavy halfton that they don't make anymore with a 6.0L gas motor) I improved gas mileage by 2 MPG by using premium over regular. I also tried a friends programer and it also improved gas mileage but I only used it for 2 tanks of fuel and then gave it back and never bought one.

The programer advanced the timing and I can't remember if it then required premium fuel or not.

You have to weigh the extra cost of premium fuel against the increased fuel mileage to determine if it is worth it.

My son and I did a science experment with a motorcycle 4 stroke engine when he was in the 6th grade and we determined that this particular engine would run longer on premium than on regular gas.

I'm going to run my new Tundra on regular for a year and then switch to premium for a year and compare. There are too many factors to get a fair comparison unless it it done for an extended period of time.