Hey everyone, been searching for a solution here. I have a 1999 XLT Ford Ranger 3.0L v6, Automatic, Normal Fuel, 180xxx miles, with a p0302 code with no other codes. This code came up about 2 years ago with some rough idling and mysteriously disappeared so I thought nothing of it at the time due to being extremely busy. A couple weeks ago, I get the same Rough Idling and throws a code pretty quickly (P0302). There was no build up to this rough idling, it just kinda started to happen and threw code immediately. It becomes more shakey around ~1500 Rpm but seems to go away past ~2000Rpm.

I have replaced
-spark plugs
-spark plugs cable
-ignition coil
-fuel filter
-#2 Fuel Injector with a brand new one, with audible clicking when running.

I have also cleaned the MAF sensor,
-taken out cleaned and tested the EGR valve,
-conducted multiple leak tests around the engine with starter fluid,
-and looked for any disconnected tubes.
When I unplug the IAC sensor, it reduces RPM but stays fine at ~850 RPM.

I have also taken the new spark plug out and tested for bright nice spark, as well as switched spark plugs and also had switched the #2 and #6 cables with no change. When I take off the #2 spark plug when running it does not seem to change. I conducted a block test 3 times that passed every time, and a compression test on all cylinders (~160-165 for #2). While driving, giving it gas seems to cause it to run smoothly, but once I reach ~55 MPH the automatic transmission seems to shift down, and the engine starts shaking immediately. To prevent this, laying on the gas, letting go and repeating seems to prevent the misfire (or shaking) from happening. I took off the valve cover as well and looked around which everything looked fine. I am keeping this truck till it dies so if I have to take apart the engine I eventually will. Or just drive with the misfire until the engine dies. It honestly feels like a vacuum leak, but I cannot find any yet. Please help because I am motivated but not a car mechanic, but I will take apart the engine myself which might not go back together well. I don't really feel like using liquid head gasket repair due to the compression test passing, but still will try it before taking the engine apart. Thank you for your time to read this and any future help