Need recommendation for a Carb for better MPG!

I have a stupid but simple solution, but it only works on my Mopars. Whenever they get low on gas I fill them. Whatever the gas price is at the time, I pay it. If needed, I skimp on eating.
That was me before I retired.
But now, my pension only pays the basics, and
my wife squanders the half of hers,
leaving the other half for groceries, and
Nothing for me.
Needless to say my teeth are falling out, cuz there's no money for that, and the car only moves when there's nothing left to eat.
What little savings I have, goes to inflation.
and yes, I am losing weight. One day soon, I will be back at what I was, at graduation.
And yes, I drive slower now, for economic reasons, namely; at 55 my car gets an easy 2mpgs better than at 65, and should an accident be imminent, I have over 15% more time/distance for evasive action, cuz if I crash the car I cannot afford to replace it, and it's a 15mile walk to the grocery store.
So you know, at 71, I'm not as comfortable as you, and you flaunting it, doesn't make me feel any better about it. But yakno, I still got my health; I mean besides my teeth falling out.............
Oh hey, I'm not complaining, nor ranting, nor accusing, nor anything; I'm jus saying.
I am just a sojourner in this World, passing thru it; for just a wisp of time I am trapped in this flesh and bone covering, and on my way to my eternal home, at the end of this present age. That's just the way it has to be. For rich or for poor, it matters not to me; for in this world, living is a temporary thing.
Enjoy it while you can.