1996 Mercury Villager bad skip or sputtering

Normally used, good running van developed a bad skip/sputter after sitting for 3 warm days in Feb. On near empty fuel tank. Thought water developed in fuel tank so I took appropriate measures (dry gas, injector cleaner & full tank of good gas). Skip/sputter hadn't cleared up and check engine light which had already been on with codes PO135-o2 sensorB181 heater problem, & PO325- knock sensor problem bank 1 prior to skip/sputter problem deveoping, began to flash while driving, but only flashed while engine was under load (driving up a grade or with a load inside). A new code dissplayed PO301-misfire cylinder no. 1 along with the 2 previously mentioned codes. I changed out cyl no. 1 fuel injector. I replaced plugs, wires, cap and rotor, and checked the timing, still nothing improved. I did a compression test and all cylinders had 185-195 psi, except for no.1 cyl which was a little over 200 psi. I checked the timing belt to see if maybe it jumped time but that checks out OK and belt is still in good condition. Only thing else that I have just noticed is that, of the new spark plugs, the no.1 cyl plug appears to be varnished and inside of no.1 cyl seems to be wet. All other cyl plugs still appear new with only 250-300 miles on them. Any ideas?