2011 Equinox misfire and reduced power

Hi y'all,
My first time on this forum. I'm having issues with a 2011 Equinox. It's showing codes P0089 and P228D. It will run fine but after driving it for a short while it will sometimes start to have a miss when coming to a stop. I checked the fuel pressure and it was between 44-62psi with the electric pump and the high pressure pump would range between 275-2001psi. I did notice that at times the desired pressure was 435-500psi and the fuel pressure was showing between 1000-2001psi. Each time it was high the fuel rail pressure command was 0 degrees. I had previously changed the spark plugs and coil boots. The vehicle has 112,622 miles on it. Any help would be appreciated.