Regarding the tune. I'm thinking factory tune is balancing act between power and the EPA folks looking out for our greater societal goodness via MPG estimates. So tune simplified pumps more gas thru injectors and to heck with MPG.
Yes it plays with timing too.
Am I mostly right or wrong?
Would 6th gear cruising at 70 be much different in MPG ?
Every tune i have had in the past actually ended up with better mpg, unless i was getting on it alot.