misfiring while in gear only?/ stiff gear shifter

This is in reguards of the same previous thread. My car (2000 v8) had been "cutting out". autozone said cylinder 3 was missfiring. They also said I might have a faulty injector. I have since then replaced the passenger side sparkplugs only do to time constraints. i had found that the oil had leaked into the spark plug hole nearest the firewall, probbably from a faulty gasket in which I have had replaced 3 or 4 years ago. I took it for a test drive and it seemed fine until the next day, same trouble. The funny thing is it seems to only do the "shuttering" while in gear and not idleing. I watch the RPM's and they do not drop when this happens. I thought for sure it was because the oil leaking but I guess not. I'm not sure of wich order the plugs are in, so I don't know if I even changed cylinder 3 yet, but surely it's not suppose to have oil anywhere there. It also seems to shutter btween 40 & 50 mph unless you stomp on it and accelerate fast.

As for the gear shifter, I called lincoln dealer and the first thing they said without looking at it was that it might be that something got spilled on it and is causing it to get stiff in cooler weather. Come to find out my wife said she spilled some pop on there awhile back. I havent had time to try to take off the console to do some cleaning nor do I know if I should. Is it easy? Any help would be very much appreciated. Very frustrated!!:banghead: I have 160k on the engine, maybe it's time to hang it up:shakehead

Rear of engine (cowl)
4 8
3 7
2 6
1 5
Front of engine (grille)

It does sound like a bad coil - which can fail without have the faulty gasket leaking oil into the well.