I drove our van to the store yesterday, I noted within about 1/4 mile that the oil pressure gauge read 80PSI. I pulled into a parking lot and contemplated.
Thought either a shorted wire or a bad oil pressure sending unit. Had my phone so I searched Youtube for 80 psi GMC Savana. It showed changing the oil pressure sending gauge. As long as I was stopped, I checked the oil, of course it was fine. So I finished my shopping trip. Today I picked up a Sending unit and 1-1/16" deep wall socket. and changed it. I had to remove two dash panels, none of the plastic broke, that's good on a 15 year old van. Then I undid the cowling, but I could not get it out, no matter what way I tuned it. Maybe you have to remove a seat, but I could not find anything about that. But I did get it turned far enough to make room to change the sensor. As soon as I started it it measured 40 PSI like it always does. It took me about 1-3/4 hours, but included tool round up and cleaning all the stuff from the cup holder and cubbyhole attached to the cowling. Not as bad as I was expecting.
This brings up a story, before I bought this van I was in the market to buy one. I went to a dealer that had a lot of used panel vans. I picked one and took it for a test drive, first thing I noticed is, it had 60 PSI on the oil pressure gauge, I thought that was a bit strange. On a whim I drove it home, about 8 miles, I got a wrench and small bowl and I drained a few tablespoons of oil from the pan. I then transferred the oil to a test tube I had and sat it upright. I then took the van back. When I returned home over half of the test tube was a thick clear liquid and the rest was oil. I suspect the motor had a rattle or knock and they filled it with STP or some other very thick clear lubricant to hide the noise. I never said anything to them, but that business was not there very long.