Rep Power: 0

So I got a 1997 Honda Civic Ex Coupe Automatic transmission and re-made d16 engine that was just put in. My problem is when i start my car and put it in gear it will go down the block with no problems till 5 mins later the trans slips and the rpm would just rev up and it wont move. When I turn off the car let it cool down for 5-10 min i start it up again and it will go back to gear and move forward like nothing happened but 1-5 mins later it slips again. Someone told me that i need to replace the trans but i need a second opinion.

 
Rep Power: 234

Check the fluid level in the tranny. Sounds like it was over-filled, which would cause the problems you're experiencing.

 
Rep Power: 0

when i got the car back after the engine was put in it was driving fine till 1-2 month later the slipping happened. Could it still be that its overfilled?? It does look like its overfilled i just checked it its over the mark. Someone also told me that i probably just need to change the fluid and transmission filter? What do you think about that??