518 Screech in neutral

Packed up is when all the friction material of a certain clutch-pack, goes into the oilpan, and the resulting all steels, weld together in a "pack". Thus the clutch is no longer a clutch at all, but a "direct-drive".
I have also seen this happen when a builder drops the front stack into the case, and fails to engage the last clutch. So then when the pump is installed, it bends and traps that clutch, and the piston cannot compress the remaining stack adequately, and so it starts out slipping dragging from day one.

I am not a transmission guy, but I'm sortof known as the guy who figures stuff out. It's a talent I was born with. This God-given gift has always paid well. Now, in retirement, it looks like a few people still remember that, and bring me strange stuff to look at.
But I don't do electronics. I did not get that gift; just mechanical.