94 grand am se 3.1 dies when put into drive

my 94 grand am se dies when i put it in dive?? the car idles in park and reverse but as soon as you put it in a forward gear it dies!! the motor is fresh , just rebuilt it and put it in ran good for about a week with a hesitation while at a steady speed but would go??? the weird thing is if the car is running and you unplug tansmission wires ,it dies??? any info im stupified!!!!