04 Redline, sudden onset misfire...
 

So, I'm officially frustrated with my redline... It has started missing under load, really badly... Plugs are freshly changed NGK 4644, I was careful to not damage the coils... It threw a P0301, but I cleared it and it hasn't returned... It runs pretty at idle and if you drive really gently, but if you use even moderate throttle, it misses... Only thing I can think of is it has a little less than a quarter tank of fuel, maybe I got crappy gas, and it's sucking the crap now(refuel with 93, add fuel system cleaner and/or seafoam), or I maybe damaged one of the coils(replace all four)... Any suggestions? The PO mentioned maybe the fuel filter, but I'm not sure if it's causing the current symptoms...

Check to make sure the cover and boots are set properly. Had that issue on my 03.
Double check the gaps. Could also be the fuel like you said. Run the fuel cleaner, change the filter, and maybe drop some octane boost in there to burn some crap off.

Doing some research, seems like plugs are the number 1 cause of this code.

These plugs don't have five miles on them... literally brand new... My father in law suggested coils, but they forked fine when I did the first plug change...

Literally, I took a friend home, car running fine, and fifteen minutes later, went to take my family to town, and the car runs like a$$...

Took different friend home in the redline tonight... Still running like crap, and the P0301 has come back as a pending code... Not sure what to try... Let the research commence!

Are those plugs 1 step colder?
Zzp suggests 2 step colder, but NGK says 1 step colder...

Where did you get the plugs and did you actually check the gap before installation? What color is your spark? I have worked at both Autozone and Advance in the past and it's not unusual for a plug to be bad out of the box. They buy seconds from the factory. And contrary to popular belief, they do NOT come pre-gapped. I don't know how many people I had to show how to gap a frigging plug over the six years I wasted between those two employers. I'd also suggest you NEVER run your gas take below 1/4 tank. If it isn't a fire problem, it's most likely fuel.

I used the 4644s that ZZP recommends, but they list as one step colder than stock... And unlike the Autolites that I was running, I did check the gap, I was in a hurry, so I didn't correct anything, but they were between .033 and .036, I consider that good enough to find out whether or not the plugs were causing the miss... The Autolites were at a much wider gap, and I thought them to be the problem...

My best guess is 5 gallons of fuel(of course the local station only has 87 so it will be dosed liberally with octane booster), and some fuel system cleaner...

Well, I could only find a 2 gallon can, so it has 2 gallons of 93, and some water remover and seafoam. I drove it a mile or two, and idles for a few minutes, no difference... Fuel gauge is sitting at a quarter tank... There is fuel at the rail, but I can't check pressure... New coils will run me $300, I'm hoping to avoid that one...

I may have an extra set of coils, I have to look.
This has me at a loss right now.