V6 Fi Vs 318

Yes, I know, it doesn't make any sense! I'm pretty sure the car has 2:76's. I had a 74 duster, (318) as a kid and without working too hard, I could get 25 mpg! Is there anyone out there that can give me a place to start as far as getting to the bottom of this problem or should I just give up and think about a 318 or ????? I have no idea. Thanks to everyone for the feedback. Tom

Wicked/Six, What would be a good strategy to get more efficiency out of my 225? Thanks! Tom