2000 T & C oil light flickering

I had the oil changed on my 2000 T&C and I noticed about 150 miles later that the oil light came on when ideling. You could increase the RPM and it woud go out. I checked the oil and it was full. I had it checked and the mechanic said they probally filled it with 5W30 instead of the 10W30. I had the oil chaned again and made sure they used 10W30. It stopped for a few days and has started again. The oil is at the correct level with no other symptons. Can someone give me an idea of how to correct this. I plan on replacing the oil sending unit to see if this corrects the problem. Thanks,