Replaced trans with new filter and fluids and seals. Replaced shift module due to it staying 2nd gear. Was running great and for some reason it will shift hard and stay in 2nd. I've reset the system by disconnecting the battery and sometimes it works. Most of the time it shifts okay till I start to slow down. When I hit 35mph it goes into 2nd and stays there. Fluid level is good. Not sure what is the issue and I'm not getting any codes.

 

Welcome to the forum.
Not sure what year of car it is, but there may be an update for the PCM that might help, just a guess though. I know there was one for the Grand Caravan due to shifting issues.