02 durango: oil gauge or oil sender?

My '02 Durango, 4.7, has 130k on it everything works fine accept stupid p0440 code but just recently my oil gauge reads at the high side of the gauge (not pegged just high), and stays their. When the truck is off but key on it reads aprox halfway. It used to fluctuate so I know something is amiss. Is it the gauge or the sender unit?

I'd definitely try the sending unit first. much easier to get to. I had a similar problem in my 5.2l Grand Cherokee and replaced the sending unit. Problem solved.