I had a '92 Yukon SLT with low oil pressure. I was told that those engines had that gremlin. I changed the sensor and it didn't help. I verified the the guage was correct with an oil pressrue tester. I would only get about 14-15 psig at idle hot and only about 20 cold and about 20 at highway speeds when warm. I started using a oil stabilizer called Hi-Tach and it brought it up about 4-5 psig from what it was. I watched it for about 60-70k miles and it never got worse until one day I got a check guages light and it was at about 4-5 psig at idle. I bit the bullet and replaced the oil pump with a high volume oil pump and from then on it ran at 20-30 psig at idle and 40-60 psig at highway speeds. Drove her about another 70k and sold it, but it was running fine.
I was told GM recommended using a Fram filter (seems like PF-35) and not to use the AC\Delco filter due to it not having a check valve at the time and Fram did. Since then GM now has a check valve to prevent drain back.
Hate to say it, but you probably need an oil pump!
The cost of the hv pump is reasonable. Seems like I replaced my oil pump without having to raise the engine. I believe there was enough clearance to drop the pan. I may be wrong, I was a teenager in the 70's
. I have a good memory, it's just short now! No, I remember now, I
thought I would have enough clearance. I had to disconnect the exhaust pipe from the exhaust manifolds and raise the engine several inches. Still only took about 4-5 hours.
Good Luck,
Dennis