1999 Dodge Durango 5.2L Oil Pressure

I have a 1999 Dodge Durango 5.2L that has 115,000 miles on it. After it's been sitting for a day or so, when I start the engine, the oil pressure guage will stay at zero for about 5 or 6 seconds, then will go up to where it seems to be working. Sometimes it stays at zero long enough for the "check gauges" light to come on for a second or two. When re-starting it after I've been running it. The guage jumps right up without any delays. The engine runs great with no other problems. It's had regular oil and filter changes. Any ideas on what might be causing this?

Thanks!