For reasons I dont know, I had a bronze/brass whatever its made of dist shaft bushing lock up on the pump drive and spin in the block, the filter got it all but it was a pain to determine where it was coming from.

Im no expert but the rpm drop would make me wonder if friction related and then bad oil.

If it were my hemi id be pulling it, too much at risk when it seems you found the problem early.

From your vid it seems like a pretty mild motor and not run too hard. Good luck with your fix.