I'm kinda getting the run around concerning potential worst case scenario costs (transmission rebuild and tq convertor replacement). The noise is definitely coming from that area, but otherwise the truck drives and shifts perfectly normal. I decided to dig a little deeper and drain the transmission and drop the pan. I found that the transmission had been overfilled by a lot. The truck calls for 16 quarts of fluid dead empty, I dropped almost that out of the transmission alone. Not good. I also found evidence of a leak from the bell housing interior.
The oil looked good, and the pan was rather clean. No evidence metal debris. I replaced the transmission filter and pan gasket, and refilled with 9 quarts of new fluid., which the truck said was right when it reached proper operating temperature. This helped, but the squeal is still there. I suspect this is either an issue with the pump or the torque convertor.
Now unless I'm missing something, it's my understanding that the 6.4 tq convertor does not have a drain and has to be removed to drain it or is this not correct? My working theory is that there may be an air bubble trapped in there that's shifting around causing the squealing. It would explain why it occasionally does it when the truck is sitting at certain angles. I can also make it go away by giving the truck more power and pushing the gas harder. I'm open to further suggestion but as a "Hail Mary" play I may just end up dropping the transmission and replacing the pump and tq convertor. I'd prefer no to do that as it doesn't look terribly fun (it really never does though).