weird oil pressure reading 2001 astro

2001 chev astro oil pressure reads extremely high roadspeed but low at an idle, Just starting doing this. I have changed the sensor but the problem still is the same. Van has 60000 kms on it. Am not sure what the problem could be. Could it be the gauge.Recently had oil changed
Thanks don63

The wild swings in the pressure reading point to the oil pressure switch, but as you said you've changed that out. It certainly could be the gauge. Replacing the gauge is not a big deal. Getting to it really is a big deal.
You might try pulling the connection at the sensor and checking to make sure it is clean and nothing is damaged. You also might trace the wires as far as you can to look for breaks in the insulation (short circuit). Assuming the wild gauge readings continued immediately after the new sensor install, it is possible that you got a defective part, it does happen.