[66Submarine]

About the fuel economy thing. My father's 66 C-10 gets around 18MPG. It has a 3.11 first gear Saginaw 4 speed manual, 3.07 gears, and a 31x10.50r15 drive tire. The engine is a flat top 350 with vortec heads, very mild sealed power CS274 RV cam, rams horn iron manifolds, and an Edelbrock 1406 (Carter copy) carb. (Runs real nice, but will spark knock if you lug it down on 87 octane. ) Generally he drives 45-55 around town and 60 or so on the highway.

So, IMO, (and IME) don't drive like there's something wrong with you, don't have a carburetor with a sunk float and the idle mixture screw falling out, and you'll get respectable mileage with these trucks.

You'll also hear about getting 10-12MPG with a 250 inline six. Again, with 3.73's, 31x10.50r15's, a 250, and a three speed, my '65 C-10 got 18+MPG, and it's so worn out it would burn a quart of 15w40 every 100 miles or so making that run @55MPH.

And, no, these numbers are in US gallons, and they are figured using google maps for the distance and filling the truck with a can and dipstick by fuel weight.

Anyway, that's been my experience, as they say, YMMV.