Random Misfire Codes and Solution to fix problem

My trooper is missing when you accelerate sitting still and driving. Misses when you go up a hill, so bad that you have to get off the road. You let off the gas it idles find. When you idle it up it starts bogging down and spatting real bad also check engine light comes on. It acts like its not getting enough fire or out of time, but it go back to idling fine. I took it to advance auto they checked the codes it read PO300 random / multiple cylinder misfire detected. You can only get to 45 MPH and 2000 - 2100 RPMs before the motor starts rattling. I have changed the spark plugs and coil boots, however it didn't fix the problem. Any suggestions on what to check next?