I can't speak for other stuff but I can speak for my '97 2.3L ranger... I've toyed with 3 different tire sizes and a couple different tread styles, mine's extended cab manual with 4.10 gears... I got it with 27" tires, more of a winter pattern not quite A/T's, got 19-21mpg, jumped up to 235 75 15's trying to get the engine turning slower for mpg, it didn't care, got a steady 21mpg but had to downshift more... then I went to a 225 70 15 in passenger tread and it'll get 21-25mpg (more miles and years with this setup) depending on use. If I'm stuck in traffic more or use it around the property idling a lot or a lot of startups it goes down, summer blend and all highway it goes up... One of the biggest things for mileage was driving style, I toyed with it, for the most part I shift at 3k and try to cruise at 2000-3000, if I'm merging I stop at 4000, that alone gained me at least 1mpg. Of course I don't always follow that but had to retrain myself...
The Geo tracker I had for a while got a steady 26mpg, was a cool rig, the Justy I had got 32... those things (both) were geared too low for constant freeway driving... wore everything out.