Engine fluttering on acceleration.

Alright, after 2 weeks of researching and dealing with this I'm finally posting to ask for help. I have a a 2010 Prius with 253K miles on it. I have never used Bars Leak or anything like it on my vehicle. 2 weeks ago it started misfiring. I took it in to the dealer and they said it was a blown head gasket causing it to misfire on cylinders 1 and 2. I spent that weekend replacing the head gaskets and cleaning the EGR Valve and EGR Cooler about 50% cleared using B-12 and a straightened coat hanger (couldn't get 100% clean due to tight schedule). Sunday night I was tired and in a rush to put it back together and forgot to clamp one of my hoses. Monday the check engine light came on and I took it to get the codes checked and it said P0420 the guy said it was my O2 sensor. Tuesday on my drive home all my coolant leaked out because of that hose I forgot to clamp. I had some left over in a bottle so I poured that in and drove it the rest of the way home (45min. drive). I spent the next week and weekend trying to get it to stop over heating and to get my heater to work. Researching on here, trying to bleed air out of the lines, pulling a vacuum, replacing the Thermostat and finally the Water Pump which was the issue. The whole time the check engine light never came back on. Replaced the water pump on Saturday, P0420 showed back up on Monday and I planned on fixing that when I got paid Friday (tomorrow). This morning on my way to work the engine started fluttering anytime I would release the gas pedal at first and then started doing it when I would accelerate too. I'm not sure what the issue is now and am hoping I haven't come full circle back to the Head Gaskets. If anyone has any insight on this it would be greatly appreciated. I'm honestly exhausted from all this.

Cody.

 

**UPDATE**
Re-checked the codes and now P0304 shows up. I also forgot to mention that I replaced the spark plugs when doing the gaskets. I'm about take the EGR Cooler back off to clean it the rest of the way, change the oil, clean the O2 Sensor, run Sea Foam through it, swap the coil pack from cylinder 4 to another one and recheck the codes. If the P0304 code is still there I'll go from there.