My first post I hope someone can help me. I have a 99 pontiac trans am. It has about 90,000 miles and as far as I no has not had any gaskets replaced nor any pumps. I am throwing a p0308 code which I already know is a 8 cylinder misfire. It all started when I was racing by doing a 2 gear pull reaching to about 100 mph against my buddy. The first run was fine but the second pull my engine lagged when I slowed down. It felt engine starved with no power and terrible shaking. I managed to get it to my house and turned my car off. Then when I started back up it ran fine. After that time the same problem would occur at random times. I figure it was the fuel filter clogged so I replaced it. Then I drove my vehicle for about a month and then it happened again but my engine started over heating and my heating gauge would be buried past 320. Let it cool then start it up but it would overheat again. I overheated the engine 4 or 5 times but no longer than a min or 2. I then diagnosed the problem and it was the thermostat stuck open. Replaced that and flushed and replaced my coolent. Then I started the car I got a random misfire code and 02 censor were reading my fuel to rich. I fixed the lean problem by replacing the elbow from the pcv to my throttle and I deleted the codes. The misfire went away until i wanted to see if everything ran good so I ripped on it and car ran beautiful until I parked the car leaving it idle for 3 minutes to get something. After 3 minutes the car started shaking and that’s when the 8 cylinder misfire happened.
Problems right before misfire (summary of top story)
Car lagging like its fuel starved after races
Replaced fuel pump
Car overheating
Replaced thermostate
Rich fuel deliver
PCV elbow replaced
Missfire 8
Attempted solutions:
Replaced spark plugs and wires with brand new ones
Changed coil packs around to see if misfire cylinder # changed (same 8 cylinder misfire)
Checked voltage on the coil pack plugs (all read the same)

The dumb move on my part was I took the engine out without doing a compression test because I barely had any skin left on my knuckles from me fitting everything else except the 8th spark plug. I tried to look at other threads but the posts stopped in mid conversation leaving me confused. If I can just get idea on where to go from their please post something.