1997 Other Chevrolet Models Typical Oil Pressure.

I have a '97 Chevy K1500, 5.7L Vortec V8. We are experiencing triple digit heat conditions right now, and I'm hoping this has some bearing on my question. What is typical oil pressure for this engine? I have only had the vehicle since February of this year, at which time it had 188,000 miles. I have checked the oil, and it looks fine. It's not burnt and it appears to be full. However, over the last three days, the oil pressure will I'm driving is up around 40psi. When I stop, it drops down to around 28 to 30 psi, sometimes a bit lower. Is this normal behavior, or do I need to park the truck and test the oil switch, or change the oil screen and oil pump?