Vibration problem

[pilotguy98]

Got a 1995 Explorer 4x4 and having some serious issues. I'm new to the forum as far as posting goes but have been watching and using threads for years and they have been a great help. My most recent problem is this stupid vibration issue. I get it at speeds from about 20 on up and its the worst when you let off the gas, especially at speeds of 55 and up. It feels like its coming from underneath the vehicle and the whole thing shakes and kind of makes a low roaring sound at the higher speeds. I used this forum to help out but im stuck now. I have replaced all ball joints, newer tires, aligned, replaced all U-joints in the rear drive shaft and just had the Transfer Case rebuilt. I pulled the Transfer case out becaue the output shaft had lots of play and when I pulled the case apart I found the output bearing was moving around so had to have the case taken to be repaired, its a common problem I found on this forum and used a place people on here have used. Got everything in last night hoping that everything was fixed, its seemed to fix everyone elses problem that was experiencing this issue. So I test drove it this morning and I STILL have the same problem. The output shaft has no play and still vibrating. What is causing this?? Am I looking at the rear axle now??