Just purchased 2004 suburban z71 with 150k miles. Clean engine- fully detailed prior to purchase. Test drive was excellent, nothing out of the ordinary. Drive home also completely normal. Later that night, drove for 30 minutes-20 minutes in oil pressure guage creeps up past 80, truck runs normally. Shut it off let it cool, everything is fine. 2 days later take it out to run errands. Engine on/ off for 3 hours at multiple stops- everything good. Take it on the highway for 10 minutes, low oil pressure light comes on. Now any time the engine gets heated and is driven for 20 minutes or more on the highway the light comes on once the truck comes down to idle. Sensor has been replaced, full oil/ filter change with Mobil 1 has been done. Still won't build pressure. Engine did shut down 1/8 mile from home, after cooling for 10 minutes started right up. Thoughts?

 

Try a mechanical oil pressure gauge to see if you are getting an accurate reading from your gauge. Hopefully it is a problem with the gauge and not the engine.