Oh, no question at all that tuning has everything to do with both performance and economy. The two go hand in hand, and you can't have either without proper tuning!

I'm going to have to call your data questionable, however. First, we can't go by what your onboard computer says. They have to be calibrated correctly to get mileage correct. I could easily set mine to read higher or lower just by changing one setting. (when I set my 49.9 mpg record, the ScanGauge had me convinced I was at over 52 mpg... it was wrong)

And the mpg you're claiming doesn't jive with your numbers, which aren't accurate enough (see first post in thread). 374 miles using 11.2 gallons would be 33.39 mpg.

So, give it another shot. Take an accurate mileage reading and exact fuel fillup reading. Do the math. See what's really going on.