need help......its time

not really under load. vibration comes after I accelerate and get to about 50-55 and then let out of it and cruise. when no acceleration. I have a slight movement in the driveshaft when I lift up on the front u-joint. it seems to be in the tailshaft. don't know exactly how much should be there but I am taking the car into the tranny shop Tuesday and let them look at it and ride with me. It is still under warranty. we will see what comes of that.