I agree, there are a lot of variables. For example, I'm guessing that TX to OH is pretty flat. Where I live you can't drive 1/4 mile without going up a hill. I've seen as much as a 5 mpg difference between going east and west on the NY Thruway because of the steady wind. I check my mpg a lot with the dash display and I can say that on the same roads at the same speeds (I play with it a lot between the toll booths between my company's offices) I picked up a solid 3 mpg on the highway after adding the exhaust. City mpg is no different. That being said, the exhaust cost $360, I installed it a few months after I got the truck, and it's probably just paying for itself now after 3 years and 60,000 miles. There are a lot things you can do that may infinitesimally increase mpg, but is there a real payback? That's the question. There is a long-standing thread at ExplorerForums.com called the Quest For 30. Guy named Aldive (R.I.P.) was bound and determined to see 30 mpg in an Explorer. I forget all the mods, he did it, but my eyes glazed over after the first 400 pages. He spent a bunch of time, effort, and money, probably never got it back, but that wasn't the point. He just wanted to see if he could do it.