Well that was a bust. Installed both of those and now don't know if I've got a bad gauge, bad sender, or a bad engine.
To start with I drove it over to the parents house to do the wrenching. Was able to catch a video of what the pressure gauge was doing. This was after about 25 minutes of driving. Not really sure how to post a video, so here's the imgur link.
When I started truck after installing, engine had been sitting for a few hours after a 30 minute drive. Not hot, but didn't take long to warm back up to operating temperature. The new gauge started out showing 44 psi and slowly dropped down to 0 at idle. I creasing rpm brought brought the gauge back up into at least the 30s, if not 40s. No engine noises that would make one suspect loss of oil pressure.
At the same time the new oil pressure sender for the dash was installed. The entire time it was running the needle stayed solid in the normal range. I know it's a dummy gauge, but with the other dropping to 0 I would have expected something to happen on the dash gauge. Even just a little flickering. Sender is not shorted to ground, I checked for that, doesn't mean it's accurate either.
So now I don't know if I have one or two inaccurate gauges and/or an engine that's about to bite the dust.
I could try a third mechanical gauge, that might tell me which gauge is more correct. I don't want a permanent install and have no idea how to route tubing without going through the firewall. That's one reason why I went electrical gauge, was easy enough to just route the wires through the door jamb.
So not really sure how to progress right now.
I know that. Knowing and doing are different things. Very easy to unintentionally use too much force with the 1/4 drive ratchet. A nut driver would be a much better tool for the job, but I'm not bullying a set of them. I need to get another 1/4 drive spinner handle, I've got every 1/4 socket I could need, except in 10mm. Used to have one, but haven't seen it in years.