Check engine light on/flashes occasionally

I would not be surprised if you needed new spark plugs. Those are some symptoms of bad spark plugs. What I would suggest is that you go back to AutoZone and get the codes scanned again. Write them down and post them on here. Then we will be doing a little less guess work and helping you to properly diagnose the problem. If you do want to check the spark plugs, here is a how-to guide: https://www.2carpros.com/articles/how-to-change-spark-plugs

And here is a youtube video: https://www.youtube.com/watch?v=UWrizXfueGU

Except what you will be doing is pulling out a plug and taking a picture or two of it to post back on here. If they are not ACDelco plugs, then I will go ahead and tell you to replace them with the proper ACDelco plugs, as those cars are very picky about their plugs.

So either get the codes or check the plugs, or do both, and get back to us. We will get you right as rain.

Ok. Never take your car to any of those chain shops. They are the worst about just replacing bunches of parts and charging you 2 arms and a leg for it. Just my experience. The P0420 code is what I'd worry the most about. That's catalyst efficiency below threshold. Basically, the catalytic converter isn't cleaning like it's supposed to. I'm attaching a basic how-to guide on replacing a catalytic converter. Some converters are welded in, and you'll probably have to get a professional to replace it. Others are bolted in and any Joe Schmoe can replace them with a couple of wrenches and some PB Blaster (WD40 on steroids - available at auto parts stores).

P0400 is for an EGR system problem, but I think you meant P0300 (misfire) since they wanted to change the plugs, wires, and ignition control module. I don't know how long you've had the car, but if the plugs and wires haven't been changed in the last 80000 miles, it's probably time to do that. The coil/control module are pretty easy to test. Simply get a spark tester (Maybe $15 at the parts store - Amazon link below) and hook it up between the coil and plug wire. Start the car and watch it light up. If one doesn't light up as brightly as the others, or simply misses sometimes, then you know it's faulty.

The P0440 code indicates some sort of problem with the fuel tank evaporative emissions system. Essentially, gas evaporates, and your car has a system to capture some of the evaporated and recycle it. There's a small leak somewhere in the system. It's not likely causing your running symptoms. So I'd address that one later, after the car is running better.

Ignition spark tester on Amazon - https://www.amazon.com/Lisle-20610-Inline-Spark-Tester/dp/B0002STSC6/ref=sr_1_3?ie=UTF8&qid=1501325755&sr=8-3&keywords=spark+tester

How to replace a cat - https://www.2carpros.com/articles/catalytic-converter-replacement

How to test a cat - https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

Symptoms of a bad cat - https://www.2carpros.com/articles/bad-catalytic-converter-symptoms

Ah ok. For the p0455, that code can sometimes be solved by changing your gas cap. It has a rubber ring seal in it that helps seal up the fuel system. When that seal gets dry rotted and cracked, fuel vapor gets lost, causing that code. A new cap costs about $10 at the local parts store, so try that before changing purge valves and other such things. Again though, this issue isn't causing your running issues. It's just causing your effective fuel economy to go down because you're losing a little bit of fuel vapor.

I'd scrap the aftermarket locking type and go with a direct fit one. I've not had good experiences with the locking ones.

Please let us know what happens so it will help others.

Cheers, Ken