Well, you'll get the BEST fuel economy at the lowest possible RPM. However, if you need to go up a hill, or something that requires more rpm, that means you will have to rev the engine up more.. which uses more fuel like that. Basically, having the engine at it'* peak torque [when your torque is low in the RPM range, of course], is best, because if you go up a hill, chances are the engine won't need extra RPM.
It'* a known fact that stale, low RPM yields higer fuel economy [IE NOT accelerating] a car gets better fuel economy at lower RPM. However just because the RPMs are low, doesn't mean you are getting the best fuel economy. Like if you are in 2nd gear.. you know that horrible gear we all dread? Well, if you have your foot to the floor, and you are at 2500 RPM, you aren't getting good fuel economy.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.