My 98 3.0 has never gotten over 19 mpg, highway or otherwise. Likely my fault, put a chip on it years ago, and one of it's functions is to richen it up a bit. Most of the time I see around 1 to 16.
Speaking of oil changes. Jan. 2010, my sister asked me if she could borrow the Ranger for a year. I had just gotten an 04 Lightning, so I let her take it. One year turned into four, it's now late 2013, my Lightning is in a body shop after being T-boned by an asshat that was in a hurry while yakking on a stupid phone. I get the Ranger back from her, finally. On the windshield is the oil change sticker from the last time I had changed it, in late 09. My sister doesn't change oil, but she never took it in for a change in four years and 40,000 + miles. And it still runs and runs great. The "oil" that came out when it was changed was absolutely black as the ace of spades and stunk badly of fuel. Didn't appear to have anything resembling viscosity. I still have it, change the oil at 5000 mile intervals, it's always used maybe a quart in a 3000 mile oil change, with the exception of the very small drip oil leak it's had forever.
So yeah, maybe most of us do change our oil too frequently. My Lightning, supercharged V-8, I don't risk it. 3000 miles and that's that. 7 quarts. My motorcycles, 3000 miles. But on them, the oil takes care of the transmission as well, so the oil is worked harder due to gears shearing the polymers.