Resonating vibration

That's an LA flexplate- very wrong for a 5.9 Magnum, and who knows what kind of aftermarket balancer.
Is this a stock 5.9 shortblock, a stroker, or what? Was it rebalanced during a rebuild? Unless it was, you got the wrong mishmash of parts for a Magnum.
Time to figure out what you've got before the motor eats itself.