I just replaced the transmission on my truck the motor ran fine before I did now as soon as I take it out of park it try's to die it idles fine but doesn't run smoothly in gear can anyone help me

 

i know this is a few weeks old. but..
was there a conector to the trans nor connected if everything is right next step i would try is disconect the battery for a few minutes then hook it back up let it idle for a few then try.