tranny problems

Hey guys what's going on? My parents got me a 95 Contour SE for Christmas and about 2 weeks ago it started acting up. Whenever I start it in the morning everything is fine, but as soon as engage reverse the RPMs drop to like 300 and surge in between that and 1000. It sounds really bad as if the car is going to die. It does this until I throw it into park or neutral or until about 20 seconds. Then when I finally give it gas to reverse it struggles as well. I let the car sit and warm up for like 5 minutes, but this does not seem to do anything. Then when I put in in drive after reverse it does the same thing. As I am accelerating the engine surges and the car sounds as if it is going to die. When the gears change to second it is not smooth at all. It sends a surge of power to second. After I have driven for a while it acts normal and later on in the day whenver I turn it on and drive everything seems fine. It only seems to act really moody after it has sat all night. The colder it gets outsidethe worse it acts up in the morning. Any ideas?

BTW this transmission is not the orignal one. It had either been replaced or rebuilt at some point. The new one has like 30k on it. I do not know the complete history being that it was bought off a lot.

when was the last fluid change?

sounds like a running problem not a tranny; check engine lamp on?