2nd gear issues with 727 transmission

I had my 727 rebuilt with a transco shift kit, manual valve body,kevlar bands, when i got the trans put back in and i went to drive the car when i shift into 2nd gear it feels like someone put on the brakes and the car comes to a stop, but if i go to 3rd gear its fine and if i bring it from 3rd back to 2nd then it again works fine, anyone have any ideas what the issue is????? i cant get the trans shop to help me thank you