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Concerning the fuel filter, this is a basic maintenance item so if never changed you can’t go wrong. I see your point concerning the P0300 vs PO303 but my thoughts are to leave no stone unturned in the search for the problem. There is one way around the replacement of the fuel filter by checking the fuel pressure with a gauge. This may be a free loaner tool from your local auto parts store. Easy to hook up on fuel rail with a quick connect fitting but wear eye protection if you decide to do this. Fuel pressure should be 53 to 59 psi per my FSM. By checking the fuel pressure you will have a greater overall understanding of your vehicle’* condition.
New plugs, designed for any particular engine that are installed are usually pre-gapped to factory specifications! Looking @ the pics of the gaps you posted, that is way beyond .060!
I agree on the gap discussion above. They don't look right.
Did you check this gap with one of those gap tools that look like a coin or some other way?
This looks like a bent electrode (not the ground hovering above it):
What tool did you use to set the gap?
Did this tool ever touch the electrode?
What model spark plug is this?
I think focusing on #3 cylinder is appropriate. If the crank sensor, oxygen sensor, or fuel filter are having issues you'd have other problems and/or the issue would show up on other cylinders. If the fuel filter were plugged enough to create an idle issue, it would hesitate at higher engine output.
What is the fuel pressure with ignition on and engine stopped?
What is the fuel pressure with the ignition on and engine idling?
What is the fuel pressure with the ignition on and engine idling and vacuum line disconnected from the fuel pressure regulator and the end of that vacuum line plugged off?
Where is #3 cylinder from your perspective (front or rear bank, and 1st, 2nd, or 3rd from the driver'* side) ?
Depending on the answers to the above, next steps might be checking compression and/or injectors.
Regarding the following:
Originally Posted by buickman32
Watching the onboard computer MPG gauge, at idle I can see it start to drop relatively quickly. Maybe from the misfire? Or most likely the computer hasnt had the chance to collect enough data.
This is expected. The computer only knows what it sees and does the math accordingly. Over-simplifying a bit here: When driving, the computer sees a certain amount of fuel get used over a certain distance and does the math. If the amount of fuel is lower proportionately to the distance, the calculated MPG number will go up. If the amount of fuel is higher proportionately to the distance, the calculated MPG number will go down. If the vehicle is sitting still idling, it is getting 0MPG. While doing this, the amount of fuel consumed will continue to increase proportionately to the distance (which is not increasing), and the calculated MPG number will go down. If the counter for MPG hasn't been reset in forever, it will go down slowly. If it has been reset recently, it will go down more quickly.
On another note: There are fake name-brand spark plugs being sold on the Internet through Amazon, Ebay, etc. Because of this, I will not buy spark plugs from these unless I'm desperate for some reason. Motorcraft plugs have been the biggest victim that I've heard of, but many other quality brands are being copied as well. Based on what I know of your situation so far, I think this isn't highly likely to be affecting your situation, but I can't rule out the possibility.
Yup! I have AC Delco 41-101. I know for a fact the new plug, singular plug on 3 is legit AC Delco but the rest are from Amazon that are most likely the fake ones. They seem to be running good for right now, but I don't know.
@CathedralCub Yes shown above. The plug in the picture is one I pulled out from cylinder 3 when I was still getting the code. They are gapped at .060 (maybe a tad bit over) but I don't really seem to be having issues. I noticed this issue before, but with the tools I had, coin gapper, I had a difficult time bending the electrode back. Again, I don't seem to be having an issue, would it throw a code if there was? I am 99% sure these are fake but I am balling on a budget right now as costs for continuing the job continue to increase.
Let me get back to you today on the fuel pressure numbers. What vacuum line is it that I should pull? The one connecting to the throttle body? The U shaped line? Or is there another line the connects behind the regulator? (Sorry for the terrible description as I am not looking at it). #3 cylinder for me is the front bank middle cylinder. My grandpa told me it is the front bank cylinder closest to the airbox. SO now I dont know what to believe and I am really glad you asked me that question.
It may be saying it is a misfire on cylinder 3 but that could be a misread. On my old 93 Buick LeSabre, I got a wrongly reported code that had me chasing the wrong rabbit for some time. Finally figured it out after wasting a lot of time on the wrong code.
I had a misfire as well one time. It turned out to be the wires; a wire set that had only been on the car for two years. Be sure to buy quality wires. Here is a trick Dad taught me; when trying to track down sparkies, look under the bonnet when it is dark. Things can show up in the dark that you can't see in the daylight. That is how I found the misfire; I could see the current travelling along the wire; really strange.
That was a catastrophic typo right there. Yes I gapped them at .060. 
