I had this problem. On my motor (1500) I took out the dizzy and drive gear
and ran the pump with a drill (counterclockwise) and got a lot of resistance.
I took my oil cooler thomostat off and it most of the resistance went away
(with the thermostat on when I stopped with the drill the pressure would spin
pump backwards a second). That experience scared me and I sh*tcanned the
thermostat and left it off.
In my case I also, at some point, got two wires crossed on my (electric) oil
pressure guage. If you're using an electric one I'd try triggering it to be
sure (touching the sender lead to ground or whatever) that it's capable of
giving you the news.
Good luck! boy I hated not seeing it go up.