Do you have vacuum advance on your distributor?
Is it hooked up?
If hooked up, does it work?
You can see if its working with a timing light.
The reason I ask these questions is I've seen more than a few cars where the owner didn't understand how important vac. advance was to gas mileage, and engine life. Sometimes they'll say " it doesn't run right with the advance hooked up" if true, they've got some thing or things adjusted wrong. You need to find a local tuning expert. Doesn't have to be a Mopar lover, just someone who understands carburetors and distributors. Looks like a great car! A stock 340 with 3.23s should get about 12mpg in town, and with a very light foot I've gotten over 20 at 55mph.
