Hi volume oil pump
I don't think the sender which is basically an on-off switch that sets at about 8 psi is going to be the issue. Probably not even there if he's plumbed an aftermarket gauge in where it used to be. Obviously he has an aftermarket gauge of some sort in there. The readings are definitely on the low side and I would not consider them acceptable by any means. The first thing to do is get another gauge and confirm the readings. I'd get a test gauge and connect it directly to the pressure port and go from there.
IIRC, the hi-press/hi-vol pumps are not adviseable for use in street Mopars, but can't remember why. In any case, I wouldn't go there to fix a low pressure issue until you confirm the actual pressure and the real state of the stock pump. BTW, mine runs more than double the numbers you quoted.
I hope you got a warranty on that rebuild. :wack: