Ok, in my experiments, I have done lots and lots of tuning. But for mpg, nothing REALLY has shown any big improvements.
One thing that I tend to avoid, but it DOES seem to help.
Open loop cruise. As you might know, I do LOTS of detailed mpg evaluations. I average around 17.6 lately (last 4 tanks of gas been dead on 17.58-17.61). Now with OL Cruise I am, amazingly enough, at 20.23. Same drive, some bad weather tossed in (rain, fog, putzy traffic) and over 600+ miles it only needed 30 gallons of 87 octane.
Can't say for sure if it is legal (likely not....) but there is some serious merit for fuel economy here.
I'll probably run like 4 tanks with OL criuse, then back to 4 tanks in normal cruise and see how it compares.