So, I've got a 1997 Merc Grand Marquis, running stock at 205,000 miles.
The first issue I have is that I changed my spark plugs and wires, the wires were replaced for B&B brand, and the spark plugs were replaced for Autolite, and this solved a misfire problem I was having generally over 50% throttle and was more noticeable in damp weather, this was done at approximately 195,000 miles. This completely solved all misfire issues and gave me noticeably higher fuel economy.

Now, about two months down the road I'm noticing a new misfire, and an audible sparking noise during high load, this misfire is noticeable in all gears, not so much while coasting but during acceleration or idle. It also seems like my alternator is failing as using any electronics in the car causes the voltage meter to drop to about 1/4 and then within the next second it spikes back to the middle of the gauge. Keep in mind the battery and terminals were changed last month.
Also, with this new misfire, my cruise control no longer engages at all.

Another issue, my OBD2 port does not allow any scanners I've tried to connect, and my engine light NEVER comes on including pre-startup light, engine light for misfire will not come on, and I also accidentally forgot to reconnect my vacuum host to my air box at one point, which caused the car to consistently die and it still wouldn't go off.

And my Mercinator's final lovely issue, power steering seems to almost come to a halt at idle / low rpm, however works flawlessly upon giving the slightest amount of throttle, and hasn't gone down in power steering fluid whatsoever, the fluid was also flushed, treated with lucas power steering fluid, flushed again and filled with regular power steering fluid.

I'd love responses for things to look into or tips on diagnosis as I'm at a loss right now.