9/10 when you spin a bearing you fuck up atleast a rod and a throw on the crank.
Are you getting new short blocks each time? Or just having the crank turned and using oversized bearings?
Do you even have a mechanical oil pressure gauge?
Do you check the bearing clearances when you reassemble? < If yes, what are they?
Have you checked the clearances on your oil pump?
Check the block for blockages in the oil passages?
Is it all stock (pistons, rods, crank etc.)? If not, did you have it balanced?