Frankly, I'd suspect bell/ engine misalignment problems. If you can get a lathe large enough to chuck up the converter, you can easily see if the hub is off or not.
With the torque converter to flex plate bolts out the torque converter spins freely when engine and trans are bolted together. No binding. If there was a misalignment wouldn't there be binding? Also three years ago the engine was swapped out with a different block.
