It isn't the floor pans.

It isn't the transmission as it does it with the clutch DISENGAGED, meaning the clutch disk is stationary

So we're down to whatever rotates when the engine is rotating but the driveshaft and transmission are not. That leaves rotating assembly, flywheel and pressure plate, plus whatever is on the accessory drives. But you said you tested with all the belts off and it still did it.

Seems to me that rather than buy new parts again and again, you pull the engine and rebalance the entire rotating assembly WITH flywheel, pressure plate and harmonic damper attached.

From the first posts it sounds like maybe the vibration started when you changed the pressure plate. So that's what I'd look at first, the balance of the entire rotating assembly.

R.