76 vette...did it come with an air pump? I know a 29 anything never did. I saw TONS of cars adn truck with dead or missing air pumps pass emmissions tests (idle test).

Not sure if the hiway mileage will be affected by intake efficiency at a given RPM. Reason being, it takes X HP to move your car down the road at Y MPH. Whether you make that HP with a 4 cylinder or a big block, at 600 rpm or 6000, X HP is still what is required. By moving the efficency up the torq curve, you may need more throttle opening to generate that HP at the given road speed, so MPG goes down. BUT if the engine is overal more powerful, then less throttle should be needed at any given rad speed, so mileage goes up. Glad to know we don't know, huh?

Thermostat - lower is better for HP, higher better for emmissions.

for better gas mileage, try overdrive - you can get a well built 700R4 for $1700 w/ converter from TCI (b&m as well). For another $100 you can add a ock up torque converter (computer is what costs the money) and get 5% more hiway mileage.