Gas is high, any fuel saving tips?

[LuckyScott]

Just wondering if anybody has some tips they can share?
My '72 Suburban gets between 13 - 14 miles per gallon.
It has the factory original 350 with 220 thousand miles on in and a turbo 350 trans. What I have done is .......
Swapped in a HEi distributer. Installed a K & N air filter. Installed dual exhaust.
I keep my tires inflated and try to use just the primaries on the quadrajet carb.

I had a chance on buying a 700r trans. with the overdrive, but just didn't have the dough to purchase it.

I don't tow anything with it, so I am wondering about doing a rear gear change (anybody done this?)
Any other tips for increasing the miles per gallon on a vehicle with the aerodynamics of a barn, and that weighs the same as a barn?