01civicTN

So I had my trans rebuilt about 12k ago but almost ever since of its hot outside and when I'm in stop and go traffic when I pull out it's almost like something's holding it back! First gear kinda drags out alittle but once it's in second gear it's fine and drives normal thru rest the gears. Any idea what it could be? It doesn't do it all the time just seems to be when im traffic and when it's hotter out