I remember getting an increase of 10 percent better mileage in my '82 Mazda pickup by switching from Dino oil to synthetic. This was done when the truck had not many miles on it.
I certainly am not an expert as to whether this would be a good idea for the older Chevy engines or not.
I also picked up 1mpg by adding a homemade air dam under the front bumper to scoot the air out to the sides rather than having it compress under the truck.
Cheers, Dean
