93 Ford Tempo Transmission problems

Working on a friend's Tempo. The transmission was recently replaced
with a used. He said that it was driving fine, but when he tried to
get on the freeway it had a hard time and he could barely maintain 60
with his foot to the floor. Ultimately, he had to be towed after
coming to a hill in town that he couldn't climb. I checked his fluid
level and it was very low. What I've noticed is that when the engine
is idling and in park that it's acting like it's in gear. The engine
won't rev, but the fluid got hot very quickly. When placed in drive or
reverse, no amount of throttle will make the vehicle move, but as soon
as the throttle is removed, the vehicle will lurch forward a couple of
inches. I'm not a Ford man and am not familiar with their
transmissions. Can anybody give me an idea what could be wrong?