I have the crappy 97 geo prizm 3 speed automatic, at 60 mph its at 3000 rpm, and 3500 rpm at 70 mph. I believe the torque converter does not lock.
its rated at 27 mpg highway, and 29 highway was the old epa estimate. so far i keep on averaging 32 mpg on the freeway on the scanguage, and thats going 60-65 mph max. I want to get it to about 35. the car has power steering so that plays a bit of factor.
All I have is an intake (with cheap filter, not K&N) and front tires pumped to 50 psi, rears at 44. other than that I have no alignment issues or brake issues thats dragging anything.
If you do lots of highway driving and not a lot of city driving, it might be worth putting in a taller final gear. Acceleration will suffer and stop-and-go fuel economy might suffer, but highway economy should improve.
I doubt the 3 speed auto TC has lockup. at highway speeds, the power steering pump is going to just circulate fluid without building pressure. losses will be barely more than the friction of the pump. that's still something though. a metro ought to be just fine without power steering as small as it is.
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"
K&N filters, and similar intake modifications whose purpose is to make the intake less restricted, would generally have no effect on highway drivers and hypermilers. The stock system with the original filter has to flow enough air to make maximum power, with wide-open throttle near redline. Highway cruising uses a small fraction of that power and a small fraction of that airflow.
Additionally, there is data showing that even a badly clogged air filter won't reduce fuel economy, just power. A clogged filter, or a less free-flowing filter vs. a more free-flowing one, may allow less air in; but to match that less air, there is less fuel used. I would guess that a severely clogged air filter would contribute additional pumping loss, energy wasted getting air into the engine; but an OEM-style filter that's not awfully clogged should be every bit as good for fuel economy as anything else.