Need recommendation for a Carb for better MPG!

I forgot you had a 5 speed ya I definitely wouldn't go any higher with rear gear, I'd be going deeper 3.23/3.55 but that's me :)

Lowest rpm don't necessarily mean most efficient rpm. It takes X amount of hp to power your car down the highway no matter what rpm your turn your engine is only making the needed hp or otherwise you'd be accelerating or decelerating not cruising at speed. Say it takes 40 hp @ 75 mph it takes a certain amount of fuel with in a narrow range to make that hp question is what are the right circumstances that it will be most efficient rpm, timing etc..