Taller gears!
 

I am going to get a transmission from a Mazda 626 with taller final gears (4.111:1 instead of my 4.388:1), and it has a taller 5th, so I will lower my 65mph rpm by a little over 400. With that, and running lean, I should be able to get into the 40mpg range!
I imagine that most people can find taller junkyard gears for their cars. I know it's not a DIY thing, unless you have the time, and tools, but it can make a big difference. I have to change my clutch anyway, so I'm doing it all at once. The standard mileage for this car is 28HWY with a 1.8L, and this one has a 2.5L.

That's a lot of rpm change for such a small gear change! 3.55 to 3.92 only changes my 65mph rpm by 200 rpm.

What are you normally turning on the freeway? What is the overdrive ratio?

The "and it has a taller 5th" part is hiding after the ratios ;). I don't remember what the ratio was for 5th, though. It's a bit of a jump from 4th to 5th, but with variable resonance induction, the engine has a good long torque curve. The gearing was made small with this car for "more fun", so 60mph is about 3,100 rpm. For the first 6 months of driving an MX-3 GS people try to change out of 5th on the freeway, and remember that that's it.
There's a guy that's figuring out a way to mate a G6 6 speed tranny to this engine. That would be awesome.

when you've got high rpms to start with, small gear changes make a big difference.