Strange cylinder 6 misfires.

I have a 02 Taurus w/ 122k miles. It recently started to have misfires. The problem occurred the first time on an uphill section on the highway. There was a metallic sound and then the engine light blinking. Crazy loss of power (i could only go like 45mph on the highway, car almost dying in idle) I looked at the spark plugs and one was completely fused shut with burned up crap.

i replaced all spark plugs and wires. Put sea foam and fuel injector cleaner in gas tank drove it for at least two new tanks worth since I suspected bad fuel at first (happened right after getting gas). Now the problem transformed into this weird behavior:

I have a rough idle with some smell of gasoline. The engine light is blinking for misfires (code says cylinder 6) a lot during that time.

However after 15-30 sec of driving with loss of power in acceleration (and again blinking engine light) the car is driving just normal. I can reach 80 mph easily and hold the speed over long periods of time. I can also accelerate just like before the problem occurred.

My mechanic said cylinder 6 has probably problems w/ the valves (after $25 diagnostic) that seems very weird to me - since I would expect that to be a permanent problem w/ loss of power also at higher speeds and continued driving.

What could that be? I do not have the money to send a mechanic on a wild goose chase (he said $1,000 for repair). I am thankful for any suggestions.