Turns off in drive

Just completed a motor swap. Vehicle idles okay seemed a little rough at first took for test drive and within half a mile vehicle said reduced engine power. I was able to get back home on flat land and let vehicle idle for a few seemed okay a little stuttering put into drive and shut off, put into reverse shut off. The vehicle has new mass airflow sensor, new catalytic converters, new o2 sensors, new fuel pump, new starter. This engine has 54,000 miles on it from a Savanah. What can it be? This has been a money pit and I want to ram it into a wall at this point! I checked the ground to fire wall and motor and it is tight. I checked ground from starter to body which also seems fine. Please help!