Honestly, if you want fuel economy, you're driving the wrong vehicles.
I've done my own testing. My truck gets the same MPG doing 55 as when I'm doing 75.
I've had the engine reworked, the exhaust reworked twice. Regular gas, premium gas, various heat ranges of spark plugs. I've coasted, accelerated only when I really needed to, even tagged "let off" points on my daily route to maximize on both.
I get 12 MPG. Period. No if and's or but's about it. So what do I do? I drive 75-80 happy with the fact that that's what I'm averaging.
The only time that I probably drop below that is in the Winter when I have to drive unusually slow and kick in the 4x4 as needed.
I'm far from a rich guy. I only make $12.75 an hour. But I'm a simple guy who likes his truck, so the crappy fuel economy doesn't bother me. Honestly, I don't even notice the gas pump in my week to week budget.
I'm 95% close to buying an SCT tuner from HemiFever. They advertise "more power, less fuel." Maybe I'll improve to 13 MPG but I'm not looking for fuel economy. I just wanna dump the death flash and let her run like a V8 should. Hell, if I dropped to 10 MPG but the engine ran much stronger, I'd be happy.
Different strokes for different folks. I'd rather a vehicle that ran like a banshee and sucked down gas like I suck down whisky over one that got better fuel economy but ran wimpy. Yes, I know new stuff gets BOTH, but I don't like new stuff. Way too much electronic control and gadgets and gizmos for my liking. And I'm speaking as a 26-year-old, LOL.