KansasRon48,
The 12 MPG is more due to the Powerglide losses than to the Rochester. 16 to 20 MPG with a fresh engine and manual transmission is achievable.
Engine RPM does not equate directly to horsepower, it only indicates the power that could be produced. The fuel usage depends more on the horsepower required to move a given load than on the RPM at which that power is developed. Does anyone think that a stovebolt going up a 10% grade gets the same milage at 3500 RPM as it does going down the same grade at 3500 RPM? Many vehicles have a higher top speed in high than in high over because they do not develop enough power at the lower RPM. Lowering the RPM does more for driver comfort than engine longevity or improved milage. I guess what I'm trying to say is that if the truck is a toy, you'll be happier with numerically lower gearing, but if it pulls heavy loads, leave it alone.
George
