I just changed my heater core and now the blinking cel came on. Scaned it and came up P0304. Which would be misfire cyl 4. I'm thinking coilpack. Anyone have other ideas?

 

If you have a 99 AEB motor its most likely the output stage (or ICM for forum talk) sitting on top of the airbox. If you want to double check its not the coil move the coil to a different cylinder and see if the misfire moves with it. If it doesn't, replace the ICM.