Goodness, I've no idea, Rusty! I've certainly never heard it before! Maybe we should try looking it up in Brewers?
(but we ARE of course, on top form; it goes without saying!)
Yes, Elle, it is in Brewers!
To cook with gas.
To meet with success, to do well.
The phrase is often used in the exclamation "now we're cooking with gas!" denoting that satisfactory progress is being made.
It emerged in the USA in the 1940's.