I've been away a while but now that I think about it; it sounds like you might have a problem with either your mechanical or ignition timing. If any one of these are a little off you will definitly experience poor gas milage and loss of power. I experienced this myself after I rebuilt my engine two years ago. When I reasymbled my engine one of my timing marks (front balance shaft) was off by two knotches of the timing belt. When I started the car it sounded ok but driving down I-95 I realize my car was topping out at 110 mhp. To make a long story short I fixed the mechanical timing issue and still noticed that I was lacking power and had poor gas milage. A friend of mine bought over his timing light and we found at the engine ignition was 10 degrees out of time. Once the timing was fix I regained the lost power and the milage went up from the lousy 19 mpg to 26mpg.