Problems with transmission - torque converter

[SoCalSlaughter]

Hey everyone, have a problem and was wondering if anyone had any ideas. I recently had my TH400 trans rebuild by a local trans shop. New case, torque converter everything. Installed it myself (to save myself $400) took it back to the shop after installed. They said everything look perfect. Truck drove awesome for about 1000 miles. Then after a start up the truck was having a vibration. Can feel it in steering wheel and side view mirrors shake. Does this in idle and in drive. And with a rev up to about 3K rpm the shutters super bad. I cant go over 65mph without it shuttering. Also shifting, at the top of the rpm band just before shift it shutters. So got under the truck, took the bottom converter cover off to look for loose bolts or flexplate cracks. Couldnt find anything. So unbolted converter from flex plate and found the converter is super loose, it can move up and down, side to side. tons of free play. Im thinking the converter bearings are shot. Any other ideas? Or why this could happen on a brand new rebuild?

- 1990 V2500 4X4 Suburban - TH400 - 5.7 350 TBI