Hmmmm..... Driveline vibrations?

[kilrfrog]

Ok. So as I said earlier, new to the site and still trying to figure out how to navigate.... so heres the Q. I have a 87 K5 rolling chassis with a 85 Jimmy body on it. I seem to get a drivetrain(?) vibration at about 25-30 mph.... tried changing rear driveshaft and yoke, new u-joints but no luck. Could possibly be in transfer case? I had the 700r-4 rebuilt about 6 mos ago... took it back and they said the tranny was fine. Any info would be greatly appreciated. Thanks.