I have a 1975 Caprice Estate wagon with a 400 small block. My engine was rebuilt about 29k miles ago; last tune up less than 15K miles (3 years) ago. I'm finding my city mpg to be single-digit and freeway mpg to be between 10-12. I typically drive with no more than one passenger and very little cargo; A/C often on when freeway driving. I typically use 87 octane fuel. Is this "normal" or should I expect better mpg?