I'd compare the old pump to the new pump when it arrives. It isn't unheard of to have a relief valve stick, but it isn't very common as far as I know.
It isn't unusual to find some metal swarf on the plug after running when it has been to a machine shop
If you are going to pull the pan for a new pickup tube, I would pull a bearing cap from the rod and main and take a look. Look at an oiling schematic and pick the bearing journal the furthest from the pump.
If the new pump. oring and pickup tube don't cure the problem, and you've verified all the galley plugs are where they are supposed to be , I'd start getting suspicious about cam bearings. Did you mention that the machine shop installed new cam bearings?
Here's an interesting post from LSTech...........look at post 12
https://ls1tech.com/forums/generatio...ure-epic-pursu