2012 Chevy Cruze low oil pressure light

I have a 2012 Chevy Cruze with 100k
miles. At about 90k on the interstate
after I had been driving at least 15
minutes the low oil pressure light
comes on. I get it taken to the dealer
and they put a mechanical gauge and
said you have 30 psi or better oil
pressure and they change the sending
unit. About 1 k miles later interstate
again warning comes on again and
again it's intermittent. Oh by the way
during normal around town going to
work store etc (not interstate) light
never comes on. Well today guess
what I got on the interstate (I now have
100k) and about 20 minutes in light
comes on again first every 2 minutes
or so then more often. Car runs great
sounds great the temp gauge doesn't
move.
What the heck is going on?