Recently on my 1994 Celica, I swapped the engine for a younger 5S. I've noticed that I'm getting terrible fuel economy. I would fill my car about $10.00 @ $2.53-70/gal. Like the other day, I filled at $2.53/gal, $10.00 = about 4 gals. I only get about 60, 70-80 miles out of that. I know that isn't right because even at 80 miles I'm getting 20 miles a gallon. Any ideas where I should look for the culprit? I realize the car is 23 years old, but I would prefer to get better mileage out of it. It's suggested 27 city, 43 highway. I am quite leadfooted but even then I don't believe it should be THAT bad.

The numbers you found are for something else, the original EPA window sticker for a '94 Celica GT 5-speed is 23 city 29 highway. So if you're flooring it all the time bouncing off red line then you could easily get to 20 or less mpg out of it. Driver mods aside other quick things to check would be your tire pressure and wheel alignment.