6.0 oil pressure issue

[77c10]

I recently swapped a 2005 6.0/4L60E into my 77 c10. The engine had 225k plus miles on it when I got it. I never personally heard it run but was told by the guy that I bought it from that it held good oil pressure but had the normal LS lifter tick at idle. I tore into and below is a list of parts I replaced.

Main bearings
Rod bearings
Oil pump
Lifters
Timing chain
front and rear seals and gaskets
oil pan gasket
head gaskets
valley pan gasket
intake gasket

My issue is that my Autometer oil pressure gauge only reads around 10psi at start up. It goes up a little when you give it gas but not as much as I think it should. I tried a secondary mechanical gauge and get basically the same reading.

I have the sending unit in the location where the factory sending unit went.
I've pulled the plug on the left front of the engine and the one above the oil filter and both puked oil while cranking.
There isn't any knocking or rattling like I think there would be if it did actually have low oil pressure.

Does anyone have anything else to try?

Thanks in advance