Truck stalls whenever put in gear, including neutral. Just had transmission changed

Hi, as the concern has arisen after transmission replacement, my concern would be about the quality and functionality of the transmission, as well as the proper application for the vehicle. Is this a remanufactured transmission? Used transmission? What vehicle did it come out of if it's used? Sounds to me that it might not be appropriate for the vehicle. Way too hard to know without knowing more about your vehicle and situation. Did somebody install the transmission for you? They should be looking at this to help you out.