I have a 1999 silverado 1500 with a 5.3 Im having oil pressure problems when cold the pressure runs about 40 while driving and idiling but once the truck gets warm it goes to about 30 while driving and 0 while idiling, but if you barley touch the gas not even 1000 rpm the pressure jumps to 20 while in drive. but if you put it in park it goes to about 20 any suggestions or information would help.

Thanks,

Most oil pressure "problems" are in the sending unit- you have to be able to trust your gages- so best thing to do is plumb in a mechanical gage to know what the real pressure is. You can "tee" it in to see if the two pressures correlate. I typically would not believe the "zero" pressure reading- based on your description.

If the gage is erratic- or sits at zero a lot- then I would replace the sending unit- either way, this gives you a place to start.

This kind of oil pressure drop is common in higher mileage engines. It is usually caused by a worn oil pump, worn bearings (excessive clearance) or a defective oil pressure relief valve.

The idea here is to see how much of a pressure drop you have Stock gauges are not particularly accurate. Install a good quality mechanical pressure gauge and observe the pressure.
The rule of thumb for older engines is a minimum of 10 psi for every 1000 rpm., up to 35-40 psi or so. But a bit more than this is better.

What kind of oil do you use, 5W-30?
You can increase pressure a bit by going to 10W-30 in winter and 10W-40 in summer.

stupid question. Is there oil in the engine?