Vehicle Information: I own a 2006 Dodge Durango Limited with the standard 4.7 V8. The car has 154k miles.

About Me: I am fairly self-reliant with repairing cars. I am, however, not great at diagnostic work. Although, this is something that I am learning with every project. I share this with the community because I am no car repair expert; I am simply good at following instructions. Any advice on the below issue would be appreciate.

Background: About a month ago, the car developed a weird idle, which felt like a periodic and random stumble. I attempted to address the issue by replacing the spark plugs. In the process, I followed the standard protocols for adding diaelectric grease to the coil pack boots. The issue did not improve. I took the car to Firestone, and they completed the diagnostic test. As a remedy, they recommend new oxygen sensors, battery, and purge valve solenoid. All four o2 sensors were replaced along with the battery and purge valve. The periodic stumble continued; however, new codes emerged: P0300 and P0303. The car was running terrible at this point. P0303 isolated an issue on the third cylinder. I identified and replaced a cracked coil pack. I also took the opportunity to clean the intake manifold. Due to error on my part, I had to replace the idle air control valve and the throttle position sensor. (Long story...please don’t ask why.) Subsequently, the P0303 code disappeared and the car started running better as long as the car was warm.

Current Issue: Here is the current issue that I cannot seem to resolved. The car has a rough idle at startup, but once warm, it runs beautifully. Computer still shows code P0300, which refers to multiple misfires.
The local auto parts store recommends that I replace the remaining (7 total) coils packs. My questions:
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