Found this somewhere, I forget where:
"If you are at 35mph and in 5th gear (Around 1800RPM in the average car), you will actually be wasting more gas than if you were in 4th or even 3rd. Every car has a certain range where it gets the best fuel economy, and it is usually right before the secondary air system opens up (on newer FI secondary intake runnersor carburated secondary "power" venturis cars with more than one barrel). Most cars have secondaries that open around 2800-3500 RPM, and this lets more air, and thus, fuel into the engine. The best RPM to be at to achieve best fuel economy is at right below this point."
I don't have a scangauge...or even a tach, somebody feel like verifying, or hopefully discrediting this statement. I usually upshift from 1st or 2nd into 4th @ 20mph. I have a 4spd std.
Dan has tested and he tells me that no matter what the slower you go in 5th the better your gas mileage, even if you're madly lugging.
I've heard that also, and it's bull****, doesn't even make sense. And you definately do not have IABs on your car, so don't worrya bout this. I don't even see the logic in why higher rpms is better. I think Jangeo and metrompg have tested this also.