Our 04 tahoe could occasionally drive 40 mins down and 40 beck with no change in oil pressure, it stays at 40. The change oil light came on, even though we weren't due for another 3 months and we don't drive too far so we weren't close to the mileage either. So we took it in, got the oil changed, but the pressure wouldn't go below 80. So we took it in to a shop, they changed the sensor and it read 40 again, no issue with the oil. We drove it yesterday 40 mins and it dropped to 18-20 and wouldn't go back up. We let it sit for a few hours and it still wouldn't go back to 40, it stayed around 18-20.

Oil pressure current reading after sitting all night, and currently warming up for 10 mins.
So what could the issue be?

 

Welcome to the forum. You need to have a mechanical pressure gauge attached in order to check to see if the instrument panel gauge is reading accurately.

 

yep, confirm the reading with a master gauge. if its low on the master gauge...the oil pump may be bad or the pick up tube may be blocked.