drive shaft help
 

Hey guys I have a problem and was hoping for some help. I have a 93 f150 ext cab w/ a 5.0 and a e4od. It has a two peice drive shaft. I had a u-joint going bad so I replace it and ever since I have had a vibration. Normally between 30 and 40 MPH. I have since replace all u-joints and the carrier bearing. Still have the vibration. The drive shaft is timed. I also thought that I may have gotten a bad u-joint, so I have replaced a second time the center u-joint. Because that was the first one that I changed.

Is there something that I might be missing. I bought all of the parts from Advanced Auto. Does this mean anything to anyone? Thanks