I have a 1997 gmc Sierra 1500 5.7 motor with 112,000 miles. I have low oil pressure at hot idle...I put a new sending unit and it didn't fix it. I put a manual gauge on it and it still shows low. I put a new oil pump and all new bearings on the crank shaft. When motor is cold I have 60 psi and when the motor warms up it gradually goes down...when drivin the truck after its warm it runs between 15 and 20 psi and at idle it's at 0 psi and the check gauges light comes on. I Need help on what to do next..

 

heated hose

 

Was there any change at all when the oil pump and bearings were changed?

If you had no change after the new parts went in then I would wonder about the cam bearings. The don't usually wear much but if they were worn you would lose pressure when things got hot. Cracks at various points could cause it too.

Other than that
Were all clearances checked on the oil pump and rod/main bearings? What type of oil are you using? Was assembly lube used (vs oil) on the rebuild? Was the oil system primed before first startup? Did this come on suddenly or slowly over time?

I know, more questions than answers but more detail might help. I am rebuilding my engine now because of the same problem. In my case obviously worn bearings.

 

Were the old bearings showing wear or excessive clearance?
If so your cam bearings are bad as well.
Cheapest fix would be a high volume std pressure oil pump. Might produce enough volume at idle but won't fix the root cause.