oil pressure sensor problems

1988 cheny 2500 5.7 liter 350

in the morning when i first start the truck the oil pressure will read about 20 but when the truck warms up it drops all the way down to 0 and the engine service light come on, the gauge doesnt drop all of the sudden its slowly drops as the engine warms, untill it hits 0

It would be best to use a mechanical gauge to verify the correct oil pressure. The oil pressure sender does go bad but a mechanical gauge will tell the real pressure.

//2000CAYukon

This is a common issue on these trucks. My '88 350 did this a few years back. While a mechanical unit is definitely better, the electronic sending unit is easy and quick to change.

I agree,, verify with a mechanical gauge.....

thanks for advice, i bought a manual gage and the pressure reads about 30 all the time, but the gage in the cluster still has the same issue, it still reads even though the sensore it is unpluged, any suggestions,

No suggestions for the problem with the gauge... but does your trucks oil need to be changed? I know on my 1995 C-1500 with a 305, everytime the oil is close to needing replacement, the pressure gauge goes nuts, start out at 60, down to 40 when i step on it when its cold. When its warmed up, it will run 35 and drop down to about 5 when i step on it.
When i have fresh oil though it stays constant 60-70

no i just changed it last month