1992 Geo Storm engine replacement

I just swapped engines in my Geo Storm. AFter replacing the engine and all major electrical components, I started it up and let it run for a few minutes before preparing to time the engine. When I sut the engine off I noticed a large amount of Transmission fluid on the floor. It is leaking out the bottom through the drain port, but I cannot determine why. Any Clues as to what I may have missed that would cause such a large leak?