tranny

i just had a used tranny put in my 95 bonniville the car has p codes today i took it to the guy who put in in and results the same later in the day drove to the store and the car would not shift write away and stumbles while driving is this a bad tranny or a wiring problem,i think the old one was not bad i rushed into getting a used one any anwers please help with this one,and by the way i have and air bag light on and anti theft abs light on,would this cause my car not to shift

Welcome to AF, what was or is the code. no way tp advise you based on the info provided, there are a multitude of possibilities here. Was it this way before, is the stumbling a misfire or trans related, we cannot tell in this environment what is happening.