Washing machine wouldn't spin, is now slamming around

I have a Kenmore 80 Series (110.23822100), both the agitator and drum stopped turning. I replaced the cogs in the agitator and the motor coupling, both of which were worn down. The drum felt stiff to turn still. I was following this video to disassemble and couldn't get the drum nut off as shown here. The drum just turns as I try to turn the nut. I skipped it and went on to remove the transmission but I'm guessing I can't get it off all the way as the drum nut is threaded onto it?

Since I had already replaced the agitator cogs and motor coupling I put it all back together and now the agitator turns and the drum spins, but when the drum stops spinning it stops so abruptly it slams around the inside of the washing machine. The drum is still hard to turn and I think something else is wrong but can't get that drum nut off for the life of me.

Any tips or suggestions on getting the drum nut off? Any ideas on what part I'm going to need for this repair once I get it off?

Thanks!