Repeated Misfiring and Excess Carbon Build-up?

[Riceplant]

Hey so I got my 'tiva at 120k miles, replaced the plugs, and wires at 121k
At about 127k, it was misfiring in cylinder 3, so I replaced the plugs, and it seemed to work again. At 129k it was misfiring again on cylinder 4. It had some extreme carbon build-up on it between the gap. I replaced that one alone. Now at 131k, cylinder 3 is misfiring. I've replaced the plug, i've switched around the spark wires, and i've changed out the distributor cap and rotor. Nothing seems to work. I've taken the plug from cylinder 1, put it into cylinder 3. Cylinder 1 ran fine still, so it's not the plug.
I can smell excess gas from the exhaust so I dont think it's a fuel delivery system, and from what I can tell theres no vacuum leak. Aside from the things i've already tested and troubleshooted, I cannot find any reason why that one singular cylinder would be misfiring now, without letting up.

If it helps, the plug I took out of cylinder 3 to replace just recently, also had carbon buildup between the gap. However cylinder 1 & 2 had none. Cylinder 4 was above average, and for sure not comparable to cylinder 1 & 2

[WmWatt]

I used to get his until I stopped cleaning and gapping the spark plugs every summer. Runs fine now. LOL I'd wipe down the ignition wires as an inexpensive possible remedy. Also crimp the clips on the ends for better contact. Note: spray the ends with WD-40 or similar light lubricant to slide the rubber cups up the wire to expose the ends. Also clean the contacts on the ignition coil. Hope that helps.

[Riceplant]

I used to get his until I stopped cleaning and gapping the spark plugs every summer. Runs fine now. LOL I'd wipe down the ignition wires as an inexpensive possible remedy. Also crimp the clips on the ends for better contact. Note: spray the ends with WD-40 or similar light lubricant to slide the rubber cups up the wire to expose the ends. Also clean the contacts on the ignition coil. Hope that helps.

Well turns out the compression is screwed. Cylinder 1, 2, and 4 were all reading 180-185~ whereas cylinder 3 read an astounding 115
So I guess to the engine swap discussion form i go lol. See how people do the engine mount without spending a fortune on machining

[WmWatt]

I had that too. Carbon buildup on the exhaust valve in cyl3 was keeping it from closing. Chemical cleaner removed the carbon and the compression went back up to normal. I think the chemical I used was called a top end cleaner, poured into the oil just before a change and the engine idled for 5 min. The instructions on the can warn not to let it idle any longer as the corrosive chemical can start eating away the aluminum in the engine block. Others add chemicals to the fuel, I think Seafoam is the name of a popular one, which cleans the engine gradually over a longer period of time.To find out if your exhaust valve is staying open take off the valve cover, turn it over, and look for carbon deposits on the underside of the cover at the cyl3 valve. That's how I dicovered mine was leaking exhaust gas. Hope that helps. Good luck.