Typical gas mileage?

Generally, what kind of gas mileage can one expect from a stock 6 cyl G van?

Worst probably could be 10
mpg with a Powerglide, 13 or 14 inch tires and a 12 bolt rear end,,,,,,

I used to get about 15 from the one I had in HS. 230 3 spd/ 3:36 rear axle.
Now 350 V8 700R4/ 4:11's around 13 if I keep my foot out of it.

,,,,,,van aint fun driving unless foot is in it,,,,,,,,,

I've had as high as 20, almost 21 mpg on the highway.  That is with a 1 barrel Carter YF carburetor on a 250 CID six cylinder with a 3 speed manual transmission equipped with an R10Q-1 overdrive (OD) pushing a 3.08 rear axle on 215 75 15 Michelins.  This was on several runs from Sacramento to Tacoma on I-5.  I checked the fuel economy carefully and have a high level of confidence in the 20 mpg number.  When I changed out rear axles to the 3.36, my fuel economy dropped by 3 mpg.  The OD did not come as original equipment in my van but it was a Regular Production Option (RPO) available to our G10s so that could qualify as a stock setup or option?
108VanGuy...

Back in the seventies, I consistently got 17 with the stock 230 and 1BBL carb......Not sure what my ratio was (probably 336)