2013 Chevrolet Silverado 5.3 oil pressure

I have a 2013 Chevrolet Silverado with the 5.3
motor the truck only has just over 83,000 miles on
it I started to have a problem with the oil pressure
dropping and check engine light coming on tell me
oil pressure sensor/performance took it to the
shop had new sensor and new oil pump put on
and got it back and now the light is back on and
it's still not carrying the right pressure when you
first start the truck the pressure runs normal after
you get it up to temp and drive it on the highway it
reads around 25psi at 70 mph and when you come
to an idle it drops to around 12psi. I'm not a
mechanic by any means but something doesn't
seem right and I dont understand with the work
I've had done I shouldn't be having this problem.