340 gas mileage

I may well be, but in this case it looks like you read the OP's question more carefully.
However... in order to define "poor" we have to know what it is, and it definitely helps to know what everyone else is getting with similar combos (and how they got there). :poke:
Well, hmmm, lol, I can't see how any of that helps. He already knows there's a problem and has described it to a T. Pointing him in a reasonable direction of diagnosing will help. How great your car runs has no bearing on his dilemma, but I yield.