Gas milage help

[Awann99]

I have a 1969 gmc longbed that I just put a new crate 350 in from jegs. I reused the original manifold and it has a late 70’s Rochester 2 Barrel carb on it. I believe it’s a 2vg. I’m not sure what the gear ratio is but it has been changed from the stock. Th 400 tranny. After taking for a few drives I calculated it getting 6.8 mpg. How in the world could I pull this up. I was wanting to drive it 60 miles three days a week to school. But it’s imposslibe with that kind of MPG.
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