I've got the Edelbrock Performer 600cfm carb on my truck, with an edelbrock Performer intake manifold, mild hydraulic cam on a 350 ... 350 TH ... 12 bolt mid-70s rear end ... I'm turning 2000 rpm at 70mph on the highway ... and getting 14 - 16 mpg.
Did you tune up the gas'air mixture on your carb? 2 screws -- turn 'em clockwise until the engine starts to run rough, counter clockwise until it smoothes out, and then 1/4 turn more counterclockwise, and you're set.
