rebuilt engine car won't go

[mpbarber]

  So I completely rebuild the engine, (1989 Ford Tempo 2.3 liter) put it back in, it starts right up and runs great. I drive it around the block and it seems fine. I go out the next day, start it up but when I drive it, it will hardly accelerate. Even when I shift it down into first with the gas pedal to the floor, it barely goes.
  I can rev the engine and it has a great response. No hesitation, missing or any other signs of engine performance issues.

I'm really stumped.

Any help would be great.