2005 2500 diesel binds when in passing gear

2005 2500 diesel binds when in passing gear I have a small shop. Ive rebuild a lot ad 46& 47 re. This 2005 48 was just rebuilt with shift kit and all the good stuff. But it binds when u use passing gear. Something holding it back on power. Motor has been checked out and turbo. But u can feel trans is binding. What did I do.lol