04 Dodge Ram torque converter issue?

My son owns a 2004 Dodge Ram Hemi. A few days ago he drove it to the store and when he went to leave it wouldn’t crank. When attempting to crank it the whole truck would shake violently. I suspected the converter was locked up and a mechanic friend of mine thought the flex plate was probably cracked around the circumference of the crank flange. We put the truck on my lift and removed the starter which looked fine but had it tested anyway and it was fine. We removed the lower dust cover and inspected all the teeth on the flex plate and they are in great shape as well. Put a pull bar on the front crank bolt to see if we could fully rotate the engine but we could only rotate it about 3/4 of the way clockwise as well as counter clockwise. We unbolted the converter from the flex plate then reinstalled the starter and now the starter spins and fires the engine right up. The converter doesn’t show any signs of bluing due to overheating. Finally we pulled the transmission. The flex plate isn’t cracked. Pulled the converter from the input shaft of the transmission and when held flat and gently shook side to side it has a lot of slop in it. You can hear something moving side to side within it and I don’t think that’s normal. I thought the front pump could possibly be locked up so I reinstalled the converter on the input shaft fully to engage the pump and can spin the converter which tells me the pump isn’t locked up. I can also spin the smaller input shaft to the transmission by hand which if I’m correct drives the gears and clutches within the gear case. I can also insert my finger in the converter and spin what I believe to be the turbine. I haven’t yet tried to spin the stator but will when I get off work today. It seems to me that something (Turbine, Stator, Oil pump or internal gears, clutches) should be locked up to cause the starter to not be able to turn the engine over. Am I missing something? Could it be something in the valve body that had the converter locked up or maybe through our removing everything we unlodged something in the converter or transmission? I’m still not sure about the internal parts moving about within the converter when shaken side to side. The needle bearings for the Turbine and Stator also look to be in great shape. Any help would be greatly appreciated.

I'm sorry, I'm not familiar with auto. transmissions. I take mine to a transmission shop when they act up.
Maybe someone knowledgeable will respond.