Need recommendation for a Carb for better MPG!

This is some pretty great perspective, and you are spot on! I didn't think of it quite like this but also thought if I could get maybe 3-5 more mpg I wouldn't have to stop for gas so much with our 16 gal. tanks. My commutes are 60 miles a day. I am very good at driving in an efficient way so I know my 340 can do better. Thank You!
There's another way to look at some mods, say for eg. Headers and duals. You could end up spend big money doing this mod from a purely mpg perspective might not be worth it, but if say your looking for some performance, could be thought of a performance mod that one day may pay for itself, same with OD. OD is more of a performance mod because it allows you run deeper gears.

But if it is to purely to save money be careful how much you spend.