you're going the wrong way about it
it helps if you actually calculate the mpg and not estimate it ("about" 200 miles on a "tank" can be anywhere from 16 to 10 mpg).
since you didn't change anything major you magic airbox and the .002 difference in plug gap won't account for any mpg increase or decrease, the only way to do it properly is to average over 3 or 4 fill-ups, add the quantity up and use the odometer reading to get the exact mpg, your variation is more likely to have been different due to your estimations rather than changes in the way your Jeep runs. It also matters a lot where you drive it, you should take the same route if you want to compare exactly the mpg and also you should drive exactly the same (shift at the same rpm, drive at the same max or min speed for the same amount of time) and travel the exact same distance.
oh, and another thing, the first time you reset the computer until if finishes the learning cycle (about 10 days to 2 weeks for the average daily driver) it will be worse on mpg and not better, it gets better the more data is collected.
